HYBRIDON INC
10-K, 1999-04-15
BIOLOGICAL PRODUCTS, (NO DIAGNOSTIC SUBSTANCES)
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                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM 10-K

            For annual and transitional reports pursuant to sections
               13 or 15(d) of the Securities Exchange Act of 1934

[X]     ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE
        ACT OF 1934

        For the Fiscal Year Ended December 31, 1998

                                       OR

[ ]     TRANSITION  REPORT  PURSUANT  TO SECTION  13 OR 15(d) OF THE  SECURITIES
        EXCHANGE ACT OF 1934

                         Commission File Number 0-27352
                                                -------

                                 HYBRIDON, INC.
                     (Exact name of Registrant as specified
                      in its certificate of incorporation)


                      Delaware                               04-3072298
           (State or other jurisdiction of                (I.R.S. Employer
           incorporation or organization)              Identification Number)

                  155 Fortune Blvd.
               Milford, Massachusetts                           01757
          (Address of principal executive offices)           (Zip Code)

                                        (508) 482-7500
                     (Registrant's telephone number, including area code)

Securities registered pursuant to Section 12(b) of the Act:  NONE

Securities registered pursuant to
Section 12(g) of the Act:                      Common Stock, $.001 par value
                                               -----------------------------
                                               (Title of Class)

Indicate by check mark whether the registrant (1) has filed all reports required
to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during
the  preceding 12 months (or for such  shorter  period that the  registrant  was
required  to file  such  reports),  and  (2) has  been  subject  to such  filing
requirements for the past 90 days.

                                 Yes [X] No [ ]

Indicate by check mark if disclosure of delinquent  filers  pursuant to Item 405
of Regulation  S-K is not contained  herein,  and will not be contained,  to the
best of registrant's  knowledge,  in definitive proxy or information  statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [ ]




<PAGE>

The   approximate   aggregate   market   value  of  the  voting  stock  held  by
non-affiliates  of the registrant was $12,146,631  million as of April 13, 1999.
For purposes of determining  this number,  5,078,083 shares of common stock held
by affiliates are excluded.

As of April 13,  1999,  the  registrant  had  15,306,825  shares of Common Stock
outstanding.

                       Documents Incorporated by Reference
                       -----------------------------------

Portions of the Registrant's Proxy Statement       Items 10, 11, 12 and 13 of 
with respect to the Annual Meeting of              Part III.
Stockholders to be held on June 8, 1999.





<PAGE>

                                 HYBRIDON, INC.
                                    FORM 10-K
                                      INDEX

PART I
Item  1.   BUSINESS...........................................................2
    HYBRIDON..................................................................2
    TECHNOLOGY OVERVIEW.......................................................2
           Introduction.......................................................2
           Conventional Drugs.................................................3
           Antisense Drugs....................................................4
    HYBRIDON ANTISENSE TECHNOLOGY.............................................4
           Medicinal Chemistries..............................................4
           Manufacturing Technology...........................................5
           Proprietary Analytical Tools.......................................5
           Regulatory Know-How................................................5
    HYBRIDON DRUG DEVELOPMENT AND DISCOVERY PROGRAMS..........................6
           The Drug Development and Approval Process..........................6
           Hybridon Drug Development and Discovery Programs...................7
    CLINICAL PROGRAMS.........................................................8
           Protein Kinase A...................................................8
           HIV-1 and AIDS.....................................................8
           Cytomegalovirus....................................................9
    PRECLINICAL PROGRAMS......................................................10
    HYBRIDON SPINOUTS.........................................................10
           MethylGene, Inc....................................................10
           OriGenix Technologies, Inc.........................................11
    CORPORATE COLLABORATIONS..................................................11
           G.D. Searle & Co...................................................11
           Medtronic, Inc.....................................................13
    THE HYBRIDON SPECIALTY PRODUCTS (HSP) DIVISION............................13
    MARKETING STRATEGY........................................................15
    ACADEMIC AND RESEARCH COLLABORATIONS......................................15
    DRUG DEVELOPMENT SERVICES.................................................16
    PATENTS, TRADE SECRETS AND LICENSES.......................................16
    GOVERNMENT REGULATION.....................................................19
           FDA Approvals......................................................19
           Other Regulation...................................................20
    COMPETITION...............................................................20
    EMPLOYEES.................................................................21

Item 2.    PROPERTIES.........................................................21
Item 3.    LEGAL PROCEEDINGS..................................................22
Item 4.    SUBMISSION OF MATTERS TO A VOTE....................................22
    EXECUTIVE OFFICERS AND SIGNIFICANT EMPLOYEES OF THE COMPANY...............22





                                        i

<PAGE>

PART II.......................................................................26
Item 5.    MARKET FOR THE COMPANY'S COMMON EQUITY AND RELATED
           STOCKHOLDER MATTERS................................................26
Item 6.    SELECTED FINANCIAL DATA............................................28
Item 7.    MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND 
           RESULTS OF OPERATIONS..............................................29
Item 7A.   QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK.........45
Item 8.    FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA........................45
Item 9.    CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND 
           FINANCIAL DISCLOSURE...............................................45

PART III......................................................................46
Item 10.   DIRECTORS AND EXECUTIVE OFFICERS OF THE COMPANY....................46
Item 11.   EXECUTIVE COMPENSATION.............................................46
Item 12.   SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT.....46
Item 13.   CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS.....................46

PART IV.......................................................................47
Item 14.   EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS
           ON FORMS 8-K.......................................................47






                                       ii

<PAGE>

                           FORWARD-LOOKING STATEMENTS

           The statements  contained in this Annual Report on Form 10-K that are
not historical are forward-looking  statements within the meaning of Section 27A
of the  Securities  Act of 1933, as amended,  and Section 21E of the  Securities
Exchange  Act  of  1934,  as  amended,   including   statements   regarding  the
expectations,  beliefs,  intentions or strategies regarding the future. Hybridon
intends  that all  forward-looking  statements  be  subject  to the safe  harbor
provisions  of the  Private  Securities  Litigation  Reform  Act of 1995.  These
forward-looking statements reflect Hybridon's views as of the date they are made
with respect to future events and financial performance, but are subject to many
risks and  uncertainties,  which could cause actual results to differ materially
from any future results expressed or implied by such forward-looking statements.
Examples of such risks and  uncertainties  include,  but are not limited to: the
obtaining of sufficient financing to maintain Hybridon's planned operations; the
timely development,  receipt of necessary regulatory approvals and acceptance of
new products; the successful application of Hybridon's technology to produce new
products;  the obtaining of proprietary  protection for any such  technology and
products;  the impact of  competitive  products  and pricing  and  reimbursement
policies;  the changing of market conditions and the other risks detailed in the
Risk Factors  section of this Annual Report on Form 10-K and  elsewhere  herein.
The Company does not undertake to update any forward-looking statements.

           See "Management's  Discussion And Analysis Of Financial Condition And
Results Of  Operations  -- Risk  Factors" for a discussion  of certain risks and
uncertainties  applicable  to  the  Hybridon  and  its  stockholders,  including
Hybridon's  need for  additional  funds to sustain  its  operations  in 1999 and
thereafter.



                                        1

<PAGE>

                                     PART I

ITEM 1. BUSINESS

HYBRIDON

Hybridon,  established in 1989, is a leader in the discovery and  development of
genetic  drugs.  These  drugs are based on  "antisense"  technology  which  uses
synthetic RNA and DNA that are designed to treat the underlying cause of disease
by stopping or  reducing  the body's  production  of proteins  that  directly or
indirectly cause disease. Hybridon also manufactures and sells synthetic RNA and
DNA,  also  called  oligonucleotides,  to third  parties  on a  contract  basis.
Hybridon's  leadership  in the  antisense  field  is  based  on  oligonucleotide
technology  it  owns  or  exclusively  licenses,   including  (a)  new  advanced
chemistries, (b) sequence selection know-how, (c) drug development know-how, (d)
innovations in the manufacturing process, (e) its fully integrated,  large scale
manufacturing  facility  and  (f)  its  experience  in  manufacturing  over  300
different compounds with various chemical modifications.


TECHNOLOGY OVERVIEW

Introduction

        The human body contains many organs,  such as the heart,  liver,  brain,
etc.,  that function  together to support life. Each organ in turn is made up of
many microscopic units called cells. Each cell produces proteins which determine
how that cell  functions  within its organ,  and  ultimately how well each organ
functions  within  the body.  Almost all human  diseases  result  from  abnormal
protein  production or altered  performance  within  individual  cells.  In some
instances,  the proteins  act  directly to cause or support a disease.  In other
instances,  the proteins  interfere  with other  proteins that prevent or combat
disease.  Traditional drugs are designed to interact with protein molecules that
support or cause  diseases.  Antisense  drugs are designed to work at an earlier
state to stop the production of disease-causing or disease-supporting proteins.

        The  information  that  controls  production  of a  specific  protein is
contained  in its  gene.  Each gene is made up of two  strands  of DNA that pair
together to form a structure  called a "double  helix."  Each strand of DNA is a
string of individual DNA building blocks, called nucleotides,  that are arranged
in a specific sequence. One of the strands contains the information that directs
the composition of the specific protein,  and is called the "coding" strand. The
other strand, the "non-coding"  strand,  contains a sequence of nucleotides that
are complementary with nucleotides on the coding strand.

        The complete  human genome  consists of over 100,000  genes and contains
the information  required to produce all human proteins.  A copy of the complete
human genome



                                        2

<PAGE>

is present in each cell,  and the  proteins  made by each cell are read from its
copy of the  genome.  Proteins  are made from  genes in two  steps.  First,  the
information  contained in the gene is read from the coding  strand of DNA into a
molecule  of  messenger  RNA.  The  messenger  RNA also  consists of a string of
nucleotides  in a specific  sequence.  This is called the  "sense"  sequence.  A
sequence that is  complementary  to the sense sequence is called the "antisense"
sequence.  Second, the cell then produces proteins based on the information that
is now recorded in the messenger RNA. The information contained in a single gene
is often read into multiple  copies of messenger  RNA,  which in turn causes the
cells to produce more copies of the protein.

        A normal cell produces a particular set of normal  proteins in the right
amount  for the body to  function  properly.  In a diseased  cell,  the wrong or
mutant  proteins  are made,  or normal  proteins  are made in the wrong  amount.
Mutant proteins occur because the DNA has changed,  either through mutation,  or
by  infection  with a virus.  Infection  with a virus can also cause the cell to
make proteins that are not coded by the human genome. This misinformation causes
the cell to produce proteins that are harmful to the body.

        Antisense technology involves the use of a strand of nucleotides, called
an oligonucleotide,  which has a specific sequence exactly complementary to that
of the messenger  RNA read from a specific  gene.  Because of the  complementary
nature of its sequence,  it binds to and inactivates the messenger RNA,  thereby
decreasing  or  eliminating  the  production  of  disease  associated  proteins.
Hybridon  believes  that drugs based on  antisense  technology  may have broader
applicability,  greater efficacy and fewer side effects than conventional  drugs
because antisense drugs are designed to intervene in the production of proteins,
rather than  intervening  after the proteins are made, and in a highly  specific
and more selective fashion.

Conventional Drugs

        Most  drugs are  chemicals  that  stimulate  or stop the  function  of a
particular molecule, usually a protein, with tolerable side effects. A drug will
cause side  effects  when it  interacts  with other  proteins in addition to the
target protein.  Therefore,  a drug that interacts with as few other proteins as
possible causes fewer side effects.

        Conventional  drugs are not well  tolerated  for the  treatment  of many
diseases  because of their  relatively low level of selectivity,  thus producing
more side effects.  Conventional  drugs bind only a few, generally two or three,
points of the target molecule.  Frequently,  sites on other non-target molecules
resemble the target binding site enough to permit the conventional  drug to bind
to some degree to the non-target molecules.  This lack of selectivity may result
in decreased effectiveness of the drug because of unwanted side effects.

        In addition,  the  development of  conventional  drugs is generally time
consuming and expensive, as thousands of compounds must be made to find the most
effective drug with the fewest side effects.



                                        3

<PAGE>

Antisense Drugs

        In contrast to conventional  drugs,  antisense drugs regulate the actual
production of proteins.  Advances in the human genome  project,  including  work
conducted by academic institutions,  biotechnology  companies and pharmaceutical
companies,  have  identified  many  targets  for  antisense  drugs.  Once a gene
associated  with  a  disease-associated  protein  is  identified,  an  antisense
oligonucleotide  can be designed and its pharmaceutical  effects can be improved
by chemical modification.  Chemically-modified  oligonucleotides may be composed
of DNA, RNA or a combination of the two.

        Because  the  sequence  of nucleic  acid bases of a  chemically-modified
antisense oligonucleotide is complementary to its target sequence on a messenger
RNA, the antisense  oligonucleotide  forms a large number of bonds at the target
site,  typically between 40 and 60. Thus, the oligonucleotide will form a strong
bond  with the  messenger  RNA read  from the  selected  gene.  A few  identical
messenger  RNA molecules may cause the cell to produce many copies of a protein;
nonetheless, a few identical  chemically-modified antisense oligonucleotides may
stop this  process.  Moreover,  an enzyme  called RNaseH has been found that can
destroy the messenger RNA that binds the  oligonucleotide.  This occurs  without
destroying the oligonucleotide  itself, thus freeing the oligonucleotide to bind
with other  identical  messenger RNA molecules  and cause  destruction  of these
molecules as well. This is called  catalytic  activity.  All of Hybridon's drugs
are designed to take advantage of this  catalytic  activity so that a relatively
small  number of antisense  molecules  can  effectively  inhibit  production  of
disease-associated proteins.


HYBRIDON ANTISENSE TECHNOLOGY

        Hybridon has  developed  and owns  antisense  technology  that  includes
important  new medicinal  chemistries,  analytical  chemistry and  manufacturing
technology.  The development of Hybridon's antisense chemistry has been directed
by Dr. Sudhir Agrawal, Hybridon's Chief Scientific Officer. Hybridon's antisense
chemistry  builds on the  pioneering  work in the  antisense  field begun in the
1970s by Dr. Paul C. Zamecnik,  a founder,  consultant and director of Hybridon.
Currently,  Dr.  Zamecnik is a Professor  Emeritus at Harvard Medical School and
has a research affiliation with the Massachusetts General Hospital in Boston.

        Medicinal  Chemistries.  Hybridon's  first antisense drug, GEM 91, which
was based on its  first-generation  phosporothioate  chemistry and differed only
slightly from native DNA, was more stable than native DNA, but was still able to
trigger the action of RNaseH for catalytic  activity.  However,  there were side
effects  caused by the  administration  of this  modified DNA into the body.  In
particular,  in the last  clinical  trial  of GEM 91 three of the nine  patients
treated  experienced  unacceptable  decreases in platelet counts thus increasing
the possibility of uncontrolled bleeding. As a result, Hybridon discontinued the
GEM 91



                                        4

<PAGE>

program.  Hybridon  has,  however,  used the  information  gained from the human
clinical  trials  of  GEM  91 to  design  its more  advanced  oligonucleotide
chemistries.

        Hybridon's  scientists  have  designed and made over twenty  families of
advanced oligonucleotide chemistries including DNA/RNA combinations, also called
hybrid or mixed backbone chemistries. Hybridon believes that antisense compounds
based  on  these  advanced   chemistries  will  show  favorable   pharmaceutical
characteristics;  thus  significantly  increasing  their  potential  therapeutic
value. These compounds are likely to have the following properties:

                      o      catalytic activity;
                      o      fewer side effects;
                      o      more stable in the body enabling a patient to take 
                             doses less frequently;
                      o      more potent, enabling a patient to be given lower 
                             doses and therefore be less expensive than 
                             first-generation drug candidates; and
                      o      ability to be given to patients different ways 
                             (such as by injection, orally, or topically).

        Manufacturing  Technology.  Hybridon's  expertise  in the  synthesis  of
chemically  modified  oligonucleotides  has  served  as  the  foundation  of its
manufacturing  technology  and  know-how.  Hybridon  has  developed  proprietary
technology, including equipment, to increase the purity of its oligonucleotides,
improve  the  efficiency  of the  production  process,  increase  the  scale  of
production and reduce the cost of drug compounds significantly.

        Proprietary  Analytical Tools. Hybridon has established analytical tools
and processes that enable it to test the purity of oligonucleotides more quickly
and accurately than traditional  methods.  Hybridon uses the information that it
obtains with its tools and processes to improve quality control,  to comply with
regulatory  requirements and to monitor absorption and stability of its drugs in
preclinical  and  clinical  trials.  Hybridon has the  capability  to provide or
support all required quality control functions.

        Regulatory  Know-How.  Hybridon personnel also have extensive experience
in navigating the regulatory process in a cost-effective manner.  Hybridon often
assists HSP customers in creating drug/devise master files and writing chemistry
and manufacturing control sections for their submissions to the FDA.






                                        5

<PAGE>

HYBRIDON DRUG DEVELOPMENT AND DISCOVERY PROGRAMS

The Drug Development and Approval Process

        The process of taking a compound from the  laboratory to human  patients
is likely to take a number of years. This process is extremely  expensive and is
rigorously  regulated  by  governmental  agencies.  In the United  States,  this
process is regulated by the Food and Drug  Administration  (the "FDA").  The FDA
requires that each drug undergo a series of trials and studies  (preclinical and
clinical) prior to considering its approval for commercial  sale. The FDA or the
company conducting the trials can discontinue  clinical trials at any time if it
is felt that the patients are being exposed to an unacceptable health risk or if
there  is not  enough  evidence  that the  drug is  effective.  The FDA may also
require a company to provide additional  information or conduct additional tests
before a drug proceeds from one phase to the next. If the FDA's concerns are not
addressed by additional  information  or tests,  the drug will not be allowed to
proceed  to the  next  phase.  The  regulatory  process  in other  countries  is
generally  similar to the process required by the FDA. The sequential  phases of
the preclinical and clinical trials and studies are described below.

o       Preclinical Studies. Preclinical studies are designed to provide data on
        the  effectiveness  and safety of the  compound  before the  compound is
        administered to humans.

o       Investigational  New Drug  Application  ("IND").  If the  data  from the
        research and preclinical studies are promising, the company will file an
        IND  with the FDA.  The IND  contains  the  results  of the  preclinical
        studies and the protocol for the first clinical  trial.  The IND becomes
        active in 30 days unless the FDA  disapproves it or requires  additional
        information. Once the IND becomes active, the company can begin clinical
        trials in humans.

o       Phase I Clinical Trials. In Phase I trials, the drug is given to a small
        group of healthy individuals or patients with the disease.  These trials
        are  designed to produce  data on the drug's  safety,  the maximum  safe
        dose, how the drug is absorbed,  distributed,  metabolized and excreted,
        as a function  of time.  In some  cases,  early  indications  suggesting
        effectiveness  can be found.  A very  small  Phase I study is  sometimes
        called a Pilot Phase I study.

o       Phase II Clinical  Trials.  In Phase II studies,  the drug is given to a
        larger  group of  patients  with the  disease  to  evaluate  the  drug's
        effectiveness  and side  effects  at doses  that  are  considered  to be
        appropriate for the larger Phase III trials that follow.

o       Phase III Clinical Trials.  These studies  generally have a large number
        of patients.  The primary purpose of a Phase III study is to confirm the
        drug's effectiveness and produce additional information on side effects.
        A Phase III study that provides data



                                        6

<PAGE>

        critical to support the  registration  of the drug with the FDA is often
        called a Pivotal Trial.

o       New Drug  Application  ("NDA").  Once Phase III studies are complete,  a
        company  will file a New Drug  Application  (NDA) with the FDA.  The NDA
        contains all of the  information  gathered  from the Phase I, II and III
        trials.  Based on the NDA,  the FDA may approve the drug for  commercial
        sale. Before approving an NDA, the FDA may require additional tests and,
        in any event, may deny an NDA if the applicable regulatory  requirements
        are not met.  Even after  approval  by the FDA,  the  company  must file
        additional  reports  about  the drug  with  the FDA  from  time to time.
        Product  approvals  may be  withdrawn  by the  FDA  if  compliance  with
        regulatory  standards is not maintained or if problems  occur  following
        initial marketing.

o       Accelerated Approval.  Drugs meeting certain criteria are candidates for
        special  consideration  during  the review and  approval  process  after
        submission of an NDA.  Accelerated  review and marketing  approval of an
        NDA is  possible  for drugs  that are  intended  to treat  persons  with
        debilitating  and   life-threatened   illnesses,   especially  where  no
        satisfactory  alternatives  are available.  The more severe the disease,
        the more likely the drug will qualify for accelerated  approval.  If the
        new drug receives accelerated  approval,  the company may be required to
        conduct specific post-marketing studies to obtain additional information
        about its safety, benefits and optimal use.

Hybridon Drug Development and Discovery Programs

        Hybridon is  focusing  its drug  development  and  discovery  efforts on
antisense compounds which incorporate its advanced chemistries for the treatment
of diseases in three major therapeutic areas: cancer,  disease caused by viruses
and diseases of the eye.

        Hybridon believes there are significant additional opportunities for the
use of  antisense,  particularly  for  the  treatment  of  cancer.  Compared  to
conventional drugs, antisense may provide:

        o      more specific therapy for cancer;
        o      more  rapid  development  of  drugs  targeting   newly-discovered
               cancer-related proteins;
        o      fewer toxic side effects,  thereby  allowing  long-term  therapy,
               either alone or in combination  with other cancer therapies (such
               as radiation or chemotherapy); and
        o      in the  case of  combination  therapy,  additive  or  synergistic
               therapeutic effects.

For these reasons,  Hybridon is exploring new antisense  targets relevant to the
treatment of cancer.




                                        7

<PAGE>

        Hybridon  plans  to  seek  corporate  collaborations  for  each  of  its
compounds in development.  Hybridon intends to proceed with its GEM 231 clinical
program for the treatment of cancer through Phase II clinical  trials,  at which
time  it  may  seek  a  corporate  collaborator.  Hybridon  generally  does  not
anticipate  proceeding  with any of its other  programs  described  below beyond
their current stages of development  without a collaborative  arrangement with a
corporate partner.


CLINICAL PROGRAMS

        Hybridon has conducted  clinical  studies in the following  areas,  with
those in more advanced stages of development described first.

Protein Kinase A

        Unlike  the  growth of  normal  human  cells,  cancer  cells  grow in an
uncontrolled and harmful manner. The protein molecule protein kinase A (PKA) has
been  implicated in the formation and growth of various solid tumors,  including
colon, ovarian, breast and lung. There are two kinds of PKA. Type I is normal in
developing  fetuses,  but its  production is abnormal in adults.  PKA type II is
found in, and is  necessary  to the health of,  normal  adults.  Certain  cancer
cells,  however,  produce  PKA type I in  adults.  Hybridon's  cancer  drug that
targets PKA, GEM 231, is designed to stop the production of the harmful PKA type
I without  interfering  with the production of PKA type II. Current cancer drugs
based on conventional mechanisms can only stop production of both types, leading
to unacceptable side effects.

        Hybridon has  conducted a Phase I clinical  study that has evaluated the
safety  of GEM 231 at  multiple  doses and  found it to be well  tolerated.  The
maximum  tolerated  dose of GEM 231 was  established  for both single  doses and
multiple  doses.  Even  high  doses of GEM 231 did not  show  the  side  effects
normally seen with current cancer treatments.  Evaluation of efficacy was not an
objective of this trial. In December 1998, Hybridon received approval to start a
Phase II Clinical  trial of GEM 231 in patients  with solid tumors which had not
responded to prior  therapy.  In addition to continuing to evaluate GEM 231 as a
single-agent  therapy,  Hybridon  plans to conduct  small Phase II studies in at
least two types of solid tumors using GEM 231 in  combination  with radiation or
other anti-tumor agents, such as Taxol.

HIV-1 and AIDS

        AIDS is caused by  infection  with the HIV-1  virus and leads to severe,
life-threatening   impairment  of  the  immune  system.  AIDS  therapy  using  a
combination of drugs has resulted in decreased  rates of death and  improvements
in the quality of life for patients with AIDS.



                                        8

<PAGE>

However,  there are increasing  reports that this therapy may be failing to give
sustained clinical benefit.  Hybridon believes this underscores the need for new
AIDS therapies.

        Hybridon has  completed a pilot Phase I clinical  study in Europe of GEM
92, Hybridon's  advanced chemistry compound for the treatment of HIV-1 infection
and AIDS.  This  study  was  designed  to  explore  the  safety  and to  provide
information  on the  absorption of GEM 92 after oral dosing and  injection.  All
doses given in the pilot study were well tolerated.  Further, GEM92 was detected
in the blood after both oral  dosing and  injection,  suggesting  that it may be
possible to develop GEM 92 as an oral drug. Hybridon believes this was the first
oral  administration  of an antisense  molecule to humans. In vitro studies have
indicated  that  GEM  92 is  additive  with  a  number  of  marketed  compounds.
Importantly, both its medicinal approach and genetic target are unique.

Cytomegalovirus

        Cytomegalovirus ("CMV") is present,  although inactive, in approximately
60% of the  general  population  in the  United  States  and in up to 90% of the
HIV/AIDS  population.  Because AIDS patients have such severely  damaged  immune
systems, advanced AIDS patients often suffer from active CMV infection. The most
frequent  active form of CMV infection in AIDS patients is CMV retinitis,  which
can result in blindness if left untreated. Active CMV infection in AIDS patients
has declined in recent years  because of the success of the current  combination
AIDS  therapy.  CMV infection is also a medical  problem in other  patients with
weak immune  systems,  such as those who have undergone  organ  transplants  and
those undergoing chemotherapy.

        Hybridon has conducted Phase I and early Phase II clinical trials of GEM
132, Hybridon's  advanced chemistry antisense  oligonucleotide for the treatment
of CMV  infection.  No clinical  studies with GEM 132 are currently  ongoing and
none are  currently  planned.  Hybridon  will  reevaluate  the status of GEM 132
development  should the current poor market conditions  improve. A competitor of
Hybridon has recently  received FDA approval to market an antisense  therapeutic
for the treatment of CMV retinitis. See "Management's Discussion And Analysis Of
Financial  Condition And Results Of Operations -- Risk Factors  --Hybridon Faces
Intense Competition, And Hybridon's Products Could Be Rendered Obsolete; Many Of
Hybridon's Competitor's Have Greater Resources And Experience Than Hybridon."






                                        9

<PAGE>

PRECLINICAL PROGRAMS

Hybridon has also conducted preclinical studies in the following areas.

<TABLE>
<CAPTION>

- -----------------------------------------------------------------------------------------------------------------------
Target                                        Primary Therapeutic                Status
                                              Indication(s)
                                              -------------
- -----------------------------------------------------------------------------------------------------------------------
<S>                                           <C>                                <C>

MDM2                                          Cancer                             Research
                                                                                 Compounds/Searle
                                                                                 Collaboration
Vascular Endothelial Growth
Factor                                        Cancer Angiogenesis                Preclinical/Seeking Partner

                                              Retinopathies (e.g.                Preclinical/Seeking Partner
                                              macular degeneration
                                              and diabetic
                                              retinopathy)

                                              Psoriasis                          Preclinical/Seeking Partner

Hepatitis C Virus                             Hepatitis; Liver                   Lead Compounds/Seeking
                                              Cancer                             Partner

- -----------------------------------------------------------------------------------------------------------------------

</TABLE>


HYBRIDON SPINOUTS

        Hybridon  has used  multiple  strategies  to fund uses of its  antisense
technology that it cannot develop at present without external funding.  Hybridon
has used one such strategy with MethylGene, Inc. and Origenix Technologies Inc.

MethylGene, Inc.

        In 1996,  Hybridon and three  Canadian  institutional  investors  formed
MethylGene,  Inc.  Hybridon  currently  owns  approximately  30% of  MethylGene.
Hybridon has granted exclusive  worldwide licenses and sublicenses to MethylGene
to develop  and market (i)  antisense  compounds  to  inhibit  the  protein  DNA
methyltransferase  for the  treatment  of any  disease,  (ii)  other  methods of
inhibiting  DNA  methyltransferase  for the  treatment  of any disease and (iii)
antisense compounds to inhibit up to two additional targets for the treatment of
cancers.  DNA  methyltransferase  is  a  protein  that  has  been  shown  to  be
overproduced  in some tumors,  such as small cell lung cancer,  colon cancer and
breast cancer.  MethylGene is obligated to purchase from Hybridon all formulated
oligonucleotides that MethylGene requires at specified prices.  Hybridon is also
performing drug development and other services for MethylGene.



                                              10

<PAGE>

        The Canadian  investors  who initially  invested in MethylGene  have the
right  to  exchange  all  (but  not less  than  all) of the  shares  of stock in
MethylGene that they initially  purchased for shares of Common Stock of Hybridon
on the basis of 37.5 MethylGene shares (for which they paid  approximately  U.S.
$56.25) for one share of Hybridon  Common Stock (subject to adjustment for stock
splits, stock dividends and the like). This option expires no later than 2001.

        MethylGene  submitted an IND in the United States and Canada in December
1998 and commenced Phase I clinical trials of its first compound,  MG98, for the
treatment of cancer in March 1999.

OriGenix Technologies Inc.

        In January 1999,  Hybridon and three  Canadian  institutional  investors
formed  OriGenix to develop and market  drugs for the  treatment  of  infectious
diseases,  with an initial focus on viral diseases.  Hybridon owns approximately
49% of OriGenix.  If certain conditions are satisfied by OriGenix,  the Canadian
investors  are  committed  to make  an  additional  investment,  at  which  time
Hybridon's ownership interest in OriGenix will be reduced to 40%.

        Hybridon  has  granted to  OriGenix  worldwide  exclusive  licenses  and
sublicenses to antisense  technology  developed by Hybridon for the treatment of
human papilloma virus and hepatitis B virus infections.  Human papilloma viruses
("HPV")  cause a variety of warts,  including  benign  genital  warts which,  if
untreated, can lead to cervical cancer. Hepatitis B infections can lead to liver
cirrhosis and cancer of the liver.  In the future,  OriGenix may negotiate  with
Hybridon for additional targets. In addition,  OriGenix is obligated to purchase
from  Hybridon  all bulk  oligonucleotides  it  requires  at  specified  prices.
Hybridon  anticipates  that it will perform drug  development and other services
for OriGenix.


CORPORATE COLLABORATIONS

        An  important  part of  Hybridon's  business  strategy  is to enter into
research and development collaborations, licensing agreements or other strategic
alliances  with  third  parties,   primarily  biotechnology  and  pharmaceutical
corporations,  to develop  certain  products.  Hybridon is a party to  corporate
collaborations with Searle and Medtronic.  Hybridon expects to retain the rights
to  manufacture   many  of  the  products  it  may  license  pursuant  to  these
collaborations.

G.D. Searle & Co.

        In January 1996,  Hybridon and Searle entered into a  collaboration  for
research and development of therapeutic  antisense  compounds.  According to the
collaboration agreement



                                       11

<PAGE>

as modified in April 1998,  targets can be selected  from those in the fields of
cancer,  cardiovascular disease and  inflammation/immunomodulation  (the "Searle
Field").

        Hybridon and Searle are currently  conducting  research and  development
relating to compounds targeting MDM2. In this project, Searle is funding certain
research  and  development  efforts at Hybridon,  and Searle and  Hybridon  have
committed  personnel  to the  collaboration.  The initial  phase of research and
development  activities  will  be  conducted  through  the  earlier  of (i)  the
achievement of certain  milestones  and (ii) January 31, 2000,  subject to early
termination  by Searle.  The  parties  may extend  the  collaboration  by mutual
agreement,  including  agreement on  additional  research  funding to be made by
Searle.

        In  addition,  Searle has the right to  designate  up to six  additional
molecular  targets  in the  Searle  Field (the  "Additional  Targets")  on terms
substantially  consistent  with the terms  applicable  to the initial  molecular
target.  Searle may exercise  this right for each of the  Additional  Targets by
paying specified cash amounts (beyond specific research payments relating to the
particular  Additional  Target)  and  purchasing  additional  Common  Stock from
Hybridon (at the then fair market value),  totaling  $10,000,000  per Additional
Target.  If Searle  designates  all of the Additional  Targets,  Searle will pay
$24,000,000  in cash and  purchase  $36,000,000  of  equity.  If Searle  has not
designated  all of the  Additional  Targets  by the time the  initial  molecular
target  reaches a  certain  stage of  preclinical  development,  Searle  will be
required to purchase up to an  additional  $10,000,000  of Common  Stock (at the
then  fair  market  value) in order to keep its  right to  designate  any of the
Additional Targets.  This payment will be credited against the equity investment
payments  made by Searle for any of the  Additional  Targets  designated  in the
future.

        Searle has exclusive rights to commercialize any products resulting from
the collaboration. If Searle elects to commercialize a product, Searle will fund
and perform  preclinical  tests and clinical trials of the product candidate and
will be responsible for regulatory approvals for, and marketing of, the product.
Hybridon has agreed to perform certain research and development work exclusively
with Searle. In addition, for each product candidate, Searle is required to make
milestone  payments to Hybridon of up to  $10,000,000  upon the  achievement  of
development  milestones.  Hybridon  also will be entitled to royalties  from net
sales  of  products  resulting  from  the  collaboration.  As long  as  Hybridon
satisfies stated manufacturing capacities and capabilities, Hybridon will retain
manufacturing  rights,  and Searle will be required to purchase its requirements
of products  from  Hybridon on an exclusive  basis at specified  prices.  Upon a
change  in  control  of  Hybridon,  Searle  would  have the  right to  terminate
Hybridon's  manufacturing rights,  although the royalty payable to Hybridon from
net sales would be increased in such event.

        If Searle designates all of the Additional  Targets or if Hybridon fails
to satisfy certain  requirements  relating to its  manufacturing  capacities and
capabilities,  Searle  will have the right to require  Hybridon  to form a joint
venture with Searle for the  development  of products in the Searle Field (other
than products relating to molecular targets that have already been



                                       12

<PAGE>

designated by Searle) to which Searle will  contribute  $50,000,000  in cash and
certain  intellectual  property  rights.  Hybridon will also contribute  certain
intellectual  property  and  technology  and, if the fair  market  value of such
technology is less that  $50,000,000,  Hybridon will, at its discretion,  either
contribute  the difference in cash or have its share of the first profits of the
joint  venture  reduced by the amount of such  difference.  Hybridon  and Searle
would each own 50% of the joint venture,  although Searle's  ownership  interest
could increase to 75% if the joint venture is established  because of Hybridon's
failure to satisfy the requirements relating to its manufacturing capacities and
capabilities.

        Under the  collaboration  Searle also purchased 200,000 shares of Common
Stock in Hybridon's initial public offering.

Medtronic, Inc.

        In May 1994, Hybridon and Medtronic entered into a collaboration to test
a drug delivery device for the potential use of delivering  Hybridon's antisense
oligonucleotides  for  the  treatment  of  Alzheimer's  disease.  The  agreement
provides that Hybridon is responsible  for the development of, and will hold all
rights  to,  any  drug  developed  in  this  collaboration,   and  Medtronic  is
responsible  for the  development  of, and will hold all rights to, any delivery
system developed in this  collaboration.  By mutual  agreement,  the parties may
extend this collaboration to other neurodegenerative  disease targets.  Hybridon
is not currently conducting any activities under this collaboration.

        As part of the  collaboration,  Medtronic  purchased  a total of 131,667
shares of Hybridon's Common Stock.


HYBRIDON SPECIALTY PRODUCTS (HSP)

        In 1996,  Hybridon formed HSP to manufacture  oligonucleotide  compounds
both  for  Hybridon's  internal  use and for  sale to  third  parties.  Hybridon
believes  the  interest  in  investigating  the  potential  of  gene  expression
modulation  technologies will continue,  and even increase,  as the use of these
technologies  for the  development  of new classes of drugs  becomes more widely
understood.  The Company's strategy is to position HSP to take advantage of this
potential  growth.  There  can  be no  assurance  that  such  strategy  will  be
successful or that industry  growth will be as  anticipated.  See  "Management's
Discussion And Analysis Of Financial Condition And Results Of Operations -- Risk
Factors  --  HSP's  Results  May  Be  Lower  Than  Currently   Anticipated"  and
"Management's  Discussion  And  Analysis Of Financial  Condition  And Results Of
Operations -- Risk Factors -- Hybridon Faces Intense Competition, And Hybridon's
Products Could Be Rendered Obsolete; Many Of Hybridon's Competitors Have Greater
Resources And Experience Than Hybridon." However,  HSP is attempting to minimize
this risk by manufacturing  oligonucleotides  for many applications at different
stages of development. HSP currently is manufacturing oligonucleotides for both



                                       13

<PAGE>

diagnostic and therapeutic applications.  HSP's customers are developing over 20
oligonucleotide drugs.

        HSP  manufactures  oligonucleotides  at its 36,000  square  foot  leased
facility,  which Hybridon believes is the only facility capable of manufacturing
large   commercial-scale   oligonucleotides.   HSP  first  began  production  of
oligonucleotide   compounds   for  sale  in  June  1996  and  had   revenues  of
approximately  $1.1  million in 1996,  $1.9  million in 1997 and $2.8 million in
1998.  HSP's  principal   customers   include  Genta/JBL   Scientific,   LaJolla
Pharmaceuticals, Inc. and MethylGene, Inc.

        HSP has developed a  manufacturing  technology  platform  which combines
multiple  methods to improve the  production  process and increase the amount of
compounds produced in a single batch. HSP has developed two separate  commercial
scale  synthesizers.  One of these  machines was developed by Hybridon alone and
the other in collaboration  with Pharmacia  Biotech.  Pharmacia has the right to
make and sell  synthesizers  based on the design developed in the  collaboration
but must also pay  Hybridon  royalties  on  sales.  Hybridon  believes  that its
synthesizers  are  the  first  commercial-scale   oligonucleotide   synthesizers
designed  for  advanced  oligonucleotide   chemistries.  In  addition,  HSP  has
developed  purification processes which use water in place of chemical solvents,
decreasing  environmental  impact and permitting  purification  of large amounts
(kilograms) of  oligonucleotides.  HSP has also  developed  processes and unique
chemicals  used in the  process,  which  HSP  believes  may  further  lower  its
production costs.

        In 1996,  Hybridon  entered into a four-year sales and supply  agreement
with the Applied  Biosystems  Division  of  Perkin-Elmer.  Under the  agreement,
Perkin-Elmer  agreed to refer potential customers to HSP, and Hybridon agreed to
purchase amidites from Perkin-Elmer for the manufacture of oligonucleotides sold
to such customers. Hybridon is also required to pay Perkin-Elmer a percentage of
the sales price paid by such customers.  In addition,  Perkin-Elmer  licensed to
Hybridon its oligonucleotide synthesis patents.

        HSP is targeting three market areas for oligonucleotides:  antisense and
non-antisense  therapeutics,  diagnostics and genetic research. Within each area
there is a large number of potential  products.  HSP is currently  manufacturing
oligonucleotides for diagnostics, therapeutics and genetic research.

        The  production of  oligonucleotides  is similar in many respects to the
chemical  synthesis used to produce  conventional  drugs.  However,  unlike many
conventional drugs,  antisense compounds used for different diseases can be made
with the same chemical  building blocks using the same  manufacturing  processes
and equipment with minimal  changes.  As a result,  the knowledge and experience
that HSP obtains  manufacturing one  oligonucleotide  compound can be applied to
the  manufacture of other  oligonucleotide  compounds for the treatment of other
diseases. This also allows several different compounds to be manufactured



                                       14

<PAGE>

in one  facility,  potentially  reducing  capital  expenditures  required in the
future and  reducing  the risks  associated  with  building a plant for a single
designated drug compound.

        HSP may need to  increase  its  manufacturing  capacity  by adding  more
oligonucleotide synthesizers in order to satisfy future internal and third-party
requirements.  In addition, in order to successfully  commercialize its drugs or
achieve  satisfactory  profit  on  sales,  HSP may be  required  to  reduce  its
production  costs.  See  "Management's  Discussion  And  Analysis  Of  Financial
Condition  And Results Of  Operations  -- Risk  Factors -- HSP's  Results May Be
Lower Than Currently Anticipated."

        Hybridon  believes that it is currently  manufacturing  oligonucleotides
according to FDA-required  Good  Manufacturing  Practices (GMP). The FDA has not
formally inspected  Hybridon's  facility and procedures and Hybridon may need to
improve its procedures in the future as production  increases.  In 1997, HSP was
one  of  two  biotechnology   companies  chosen  to  participate  in  the  FDA's
Biotechnology  PAI Pilot  Initiative.  This is a pilot  program  that allows FDA
regulatory  officials to provide advice on compliance with FDA standards  before
companies submit drug approval filings.


MARKETING STRATEGY

        Hybridon plans to market the drugs it is developing either directly with
its own sales group or through  co-marketing,  licensing,  distribution or other
arrangements with pharmaceutical and biotechnology companies. To market products
that will serve a large,  geographically  diverse patient  population,  Hybridon
expects to enter into  licensing,  distribution  or partnering  agreements  with
pharmaceutical  and biotechnology  companies that have large,  established sales
organizations. While Hybridon has developed general marketing strategies, it has
not begun to implement any of these strategies. See "Management's Discussion And
Analysis  Of  Financial  Condition  And  Results  Of  Operations--Risk   Factors
- --Hybridon's Lack Of Marketing  Experience Could Adversely Affect Its Ability To
Commercialize Its Drugs."


ACADEMIC AND RESEARCH COLLABORATIONS

        Hybridon  enters into  collaborative  research  agreements  for specific
disease  targets  and  other  research  activities  in order to  supplement  its
internal research capabilities and to obtain access to the specialized knowledge
or  expertise.   In  some  cases   Hybridon   relies   primarily   upon  outside
collaborators.  Accordingly,  termination of a collaborative  research agreement
could result in the termination of the related research program.

        In  general,   Hybridon's   collaborative  research  agreements  require
Hybridon  to pay  various  amounts to support  the  research.  Hybridon  usually
provides the oligonucleotides,



                                       15

<PAGE>

which the  collaborator  then tests. If the  collaborator  creates any invention
during  the  course of his or her  efforts,  solely or  jointly  with  Hybridon,
Hybridon  generally  has  an  option  to  negotiate  an  exclusive,   worldwide,
royalty-bearing  license  to  the  invention.  Inventions  developed  solely  by
Hybridon's  scientists  as  part  of  the  collaboration   generally  are  owned
exclusively by Hybridon. Most of these collaborative agreements are nonexclusive
and can be cancelled on short notice.

        Since July 1997,  as part of its  restructuring,  Hybridon has allowed a
number of its  collaborative  research  agreements to expire and has  terminated
certain  others,  but has maintained  those which it believes are appropriate to
support its current drug development programs.


DRUG DEVELOPMENT SERVICES

        Hybridon's Drug Development  Department has experience in the design and
conduct of  preclinical  studies and has prepared and  submitted the reports and
other  regulatory  documents for Hybridon's three advanced  chemistry  antisense
compounds which have entered Phase I studies. This development expertise is also
being used  through a contract  with  MethylGene  under  which  Hybridon's  Drug
Development Department has helped design and monitor the preclinical studies for
MethylGene's antisense compound,  MG98, leading to MethylGene's submission of an
Investigational  New Drug ("IND")  application  in Canada and the United States.
MethylGene compensated Hybridon for these services.  Hybridon expects to perform
similar services for OriGenix.


PATENTS, TRADE SECRETS AND LICENSES

        Proprietary  protection for Hybridon's products,  processes and know-how
is important to Hybridon's  business.  For that reason,  Hybridon prosecutes and
aggressively enforces its patents and proprietary technology.  Hybridon's policy
is  to  file  patent   applications  to  protect   technology,   inventions  and
improvements  that are considered  important to the development of its business.
Hybridon  also relies upon trade  secrets,  know-how,  continuing  technological
innovation and licensing  opportunities  to develop and maintain its competitive
position.

        As of March 1, 1998,  Hybridon owned or  exclusively  licensed 62 issued
U.S. patents,  9 issued foreign patents, 7 allowed U.S. patent  applications,  2
allowed  foreign  applications  and 63 other U.S. and 99 other  non-U.S.  patent
applications.  The patents and applications  cover various  chemically  advanced
oligonucleotides,  target sequences,  specific oligonucleotide products, methods
for making and purifying  oligonucleotides,  analytical  methods and methods for
antisense  treatment of various  diseases.  The patents  expire at various dates
ranging from 2006 to 2015.




                                       16

<PAGE>

        Hybridon is the worldwide,  exclusive licensee under several U.S. issued
or allowed  patents and  various  patent  applications  owned by  University  of
Massachusetts  Medical Center  (formerly the Worcester  Foundation)  ("U. Mass")
relating to oligonucleotides and hybrid or mixed backbone  chemistries.  Many of
these patents and patent applications have corresponding applications on file or
corresponding patents in other major industrial countries.

        One of the issued U.S.  patents (the "HIV Patent") and one of the issued
European patents licensed from the U. Mass cover antisense  oligonucleotides  as
new compositions of matter for stopping the replication of HIV. The other issued
U.S.  patents include claims covering  composition and uses of  oligonucleotides
based  on  advanced   chemistries,   methods  of   oligonucleotide   production,
compositions of certain modified oligonucleotides that are useful for diagnostic
tests  or  assays  and  methods  of  purifying  oligonucleotides.  The  earliest
expiration of the patents  licensed to Hybridon by U. Mass is 2006, when the HIV
Patent expires.

        Hybridon  also is the  exclusive  licensee  under various other U.S. and
foreign patents and patent applications,  including two U.S. patent applications
owned   by   McGill   University   relating   to   oligonucleotides    and   DNA
methyltransferase.  Hybridon and Massachusetts  General Hospital ("MGH") jointly
own one issued U.S. patent applicable to Alzheimer's disease.  Hybridon holds an
exclusive license to MGH's interests under such patent.

        Hybridon  is a  nonexclusive  licensee  of certain  patents  held by the
National    Institutes   of   Health   ("NIH")   relating   to   oligonucleotide
phosphorothioates  and a  nonexclusive  licensee of an NIH patent  covering  the
phosphorothiolation  of  oligonucleotides.  The field of each of these  licenses
extends to a wide variety of genetic targets.

        The U.S. Patent and Trademark  Office (the "PTO") has informed  Hybridon
that certain patent applications  exclusively  licensed by Hybridon from U. Mass
have  been  submitted  to the  Board of  Patent  Appeals  and  Interferences  to
determine  whether an interference  should be declared with issued U.S.  patents
held by the NIH relating to oligonucleotide phosphoro-thioates.  An interference
proceeding  is a proceeding in the PTO to determine who is the first to invent a
claimed  invention,  and thus who is  entitled  to a patent  for the  invention.
McDonnell Boehnen Hulbert & Berghoff,  Hybridon's U.S. patent counsel, is of the
opinion that the U. Mass patent  application has a prima-facie case for priority
against  the  NIH  for  an  invention  that  includes  phosphorothioate-modified
oligonucleotides.  However,  there can be no assurance an  interference  will be
declared,  or if declared,  as to the outcome thereof.  If Hybridon were to lose
the   interference,   its   nonexclusive   license  from  the  NIH  of  the  NIH
phosphorothioate patents would not be affected.

        The  PTO  has  also  declared  a  four-way  interference  involving  two
additional U.S. patents relating to Hybridon's chimeric  oligonucleotides  which
Hybridon  exclusively  licenses from U. Mass.  This  interference  also involves
patents owned by or exclusively licensed to Integrated DNA Technologies ("IDT"),
Isis Pharmaceuticals, Inc. and Gilead Sciences, Inc.



                                       17

<PAGE>

All parties have agreed to settle the interference, and the settlement agreement
has been filed with the PTO for  approval.  In connection  with the  settlement,
Hybridon has obtained a license to certain patents and patent applications owned
by IDT which broadly claim chemical modifications to oligonucleotides.  Hybridon
has also granted a license to IDT to make,  use and sell limited  quantities  of
oligonucleotides which incorporate certain of Hybridon's advanced chemistries.

        Under its  licenses,  Hybridon is obligated to pay  royalties on its net
sales of products or processes  covered by the licensed  technology  and in some
cases to pay a percentage  of any  sublicense  income that Hybridon may receive.
These licenses  impose various  commercialization,  sublicensing,  insurance and
other  obligations  on  Hybridon.  Failure  of  Hybridon  to comply  with  these
requirements could result in termination of the license.

        The  patent  positions  of  pharmaceutical   and  biotechnology   firms,
including  Hybridon,  are  generally  uncertain  and involve  complex  legal and
factual  questions.   Consequently,  even  though  Hybridon  and  its  licensors
prosecute their patent  applications,  Hybridon does not know whether any of the
applications  will issue as patents or, if any patents are issued,  whether they
will provide adequate proprietary  protection.  Since patent applications in the
United  States  are  maintained  in  secrecy  until  patents  issue,  and  since
publication of discoveries  in the scientific or patent  literature  tend to lag
behind actual discoveries by several months, Hybridon cannot be certain that it,
or any licensor of patents to it, was the first creator of inventions claimed by
pending patent  applications or that Hybridon or any licensor,  was the first to
file patent applications for such inventions.  See "Management's  Discussion And
Analysis Of Financial  Condition  And Results Of  Operations  -- Risk Factors --
Hybridon May Be Unable To Obtain Or Enforce Patents; Its Patents May Not Provide
Adequate Protection."

        Hybridon's  competitors  and other third parties hold issued patents and
pending patent  applications  relating to antisense  and/or  particular  genetic
targets  which could require  Hybridon to change its products or processes,  pay
substantial  licensing  fees or cease  certain  activities,  including an issued
patent in Europe  covering  MDM2 (the "MDM2  Patent").  Hybridon is currently in
license  negotiations  with the  holder  of the  MDM2  Patent.  There  can be no
assurance that Hybridon will be able successfully to obtain any such licenses at
a reasonable  cost or that  licenses to such  intellectual  property will not be
made available to competitors of Hybridon on an exclusive or nonexclusive basis.
Failure  to  obtain  such  licenses  could  have a  material  adverse  effect on
Hybridon.  See "Management's  Discussion And Analysis Of Financial Condition And
Results Of  Operations  -- Risk  Factors -- Hybridon  May Be Unable To Obtain Or
Enforce Patents; Its Patents May Not Provide Adequate  Protection."  Previously,
another  European  patent had been granted to a third party  relating to certain
types of stabilized synthetic oligonucleotides for use as therapeutic agents for
selectively  blocking the translation of a messenger RNA into a targeted protein
by binding with a portion of the messenger RNA to which the stabilized synthetic
oligonucleotide is substantially complementary. This European patent was revoked
in entirety in an opposition



                                       18

<PAGE>

proceeding  before the European  Patent Office in September  1995. The holder of
this patent  appealed such  decision.  This appeal was dismissed on February 18,
1999.

        Hybridon  requires  its  employees,   consultants,   outside  scientific
collaborators   and  sponsored   researchers   and  other  advisors  to  execute
confidentiality  agreements.  These  agreements  provide  that all  confidential
information  developed or made known by Hybridon to the individual is to be kept
confidential,  subject to specific  exceptions.  In the case of  employees,  the
agreements  provide  that all  inventions  conceived by the  individual  are the
exclusive  property of  Hybridon.  There is no  assurance,  however,  that these
agreements will provide  meaningful  protection for Hybridon's  trade secrets or
adequate remedies in the event of breach of agreement.

        Hybridon engages in collaborations and sponsored research agreements and
enters into  preclinical  and  clinical  testing  agreements  with  academic and
research  institutions and U.S.  government  agencies,  such as the NIH, to take
advantage of their technical expertise and to gain access to certain technology.
Consistent with pharmaceutical industry and academic standards, these agreements
may  provide  that  developments  and  results  will be freely  published,  that
information   or  materials   supplied  by  Hybridon  will  not  be  treated  as
confidential  and that  Hybridon  may be  required  to  negotiate  a license  to
developments and results in order to commercialize  products incorporating them.
There can be no assurance that Hybridon will be able  successfully to obtain any
such license at a reasonable cost or that such developments and results will not
be made  available to  competitors  of Hybridon on an exclusive or  nonexclusive
basis. See "Business -- Academic and Research  Collaborations."


GOVERNMENT REGULATION

        Hybridon's  research,  clinical development and production are regulated
for safety,  effectiveness and quality by numerous  governmental  authorities in
the United States and other countries.  Hybridon believes that it is in material
compliance with all applicable  federal,  state and foreign legal and regulatory
requirements.  However, it is possible that legal or regulatory requirements may
change,  which could have a material  adverse  effect on Hybridon's  business or
results of operations.

FDA Approvals

        In addition to product approvals by the FDA as described above, Hybridon
may be  required  to  obtain  a  satisfactory  inspection  by the  FDA  covering
Hybridon's  manufacturing  facilities before a product  manufactured by Hybridon
can  be  marketed  in  the  United  States.   The  FDA  will  review  Hybridon's
manufacturing procedures and inspect its facilities and equipment for compliance
with GMP and other applicable rules and regulations. Any material


                                       19

<PAGE>

change by Hybridon in its  manufacturing  process,  equipment or location  would
necessitate additional FDA review and approval.

Other Regulation

        In addition to regulations enforced by the FDA, Hybridon also is subject
to regulation under the Occupational Safety and Health Act and other present and
potential  future  federal,  state or local  regulations.  In addition,  because
Hybridon uses hazardous  materials,  chemicals,  viruses and various radioactive
compounds,  Hybridon's must comply with U.S.  Department of  Transportation  and
Environmental  Protection  Agency  requirements  and  other  federal,  state and
foreign laws and regulations  regarding hazardous waste disposal,  air emissions
and waste-water discharge.  Although Hybridon believes that it complies with the
standards prescribed by applicable  regulations,  it cannot completely eliminate
the risk of  accidental  contamination  or injury from these  materials.  In the
event of such an  accident,  Hybridon  could be held liable for any damages that
result. Any such liability could have a material adverse effect on Hybridon.


COMPETITION

         Hybridon's  proposed products will be competing with products developed
by third parties for the same diseases. Competition among these products will be
affected  by,  among  other  things,  product  efficacy,  safety,   reliability,
availability,  price and  patent  protection.  In  addition,  the speed at which
Hybridon  can  develop  products,  complete  the  clinical  trials and  approval
processes and supply commercial quantities of the products to the market will be
an important  competitive  factor.  Hybridon's  competitive  position  will also
depend  upon its ability to attract and retain  qualified  personnel,  to obtain
patent protection or otherwise develop proprietary products or processes, and to
secure sufficient funds to sustain it until commercial sales of its drugs occur.

        There are a number of companies,  both privately and publicly held, that
are conducting research and development  activities on technologies and products
aimed at therapeutic  regulation of gene expression,  including antisense drugs.
Hybridon  believes that the  industry-wide  interest in these  technologies  and
products  will  continue and will  accelerate.  It is possible  that  Hybridon's
competitors  will succeed in developing  products that are more  effective  than
Hybridon's or which would render Hybridon's  technology and products obsolete or
noncompetitive. One competitor of Hybridon has recently received FDA approval to
market an antisense therapeutic product for the treatment of CMV retinitis.  See
"Management's  Discussion  And  Analysis Of Financial  Condition  And Results Of
Operations -- Risk Factors -- Hybridon Faces Intense Competition, And Hybridon's
Products Could Be Rendered Obsolete; Many Of Hybridon's Competitors Have Greater
Resources And Experience Than Hybridon." Furthermore, because of the fundamental
differences between



                                       20

<PAGE>

antisense  and other  technologies,  there may be diseases  for which such other
technologies are superior to antisense.

        Hybridon  has  many   competitors,   including,   among  others,   major
pharmaceutical and chemical  companies,  biotechnology  firms,  universities and
other  research  institutions.  Many of  these  competitors  have  substantially
greater  financial,  technical and human  resources than Hybridon.  In addition,
many of these competitors have significantly greater experience than Hybridon in
undertaking  preclinical studies and human clinical trials of new pharmaceutical
products and obtaining FDA and other regulatory approvals of products for use in
health  care.  Accordingly,  Hybridon's  competitors  may  succeed in  obtaining
regulatory  approvals for products more rapidly than Hybridon.  Furthermore,  if
Hybridon  receives  approval to commence  commercial sales of products,  it will
also be  competing  with  respect  to  manufacturing  efficiency  and  marketing
capabilities, areas in which it has limited experience.

        HSP also  competes  against  a number  of  third  parties.  There is the
possibility  that  Hybridon's  customers  could  begin to  produce  their  drugs
internally or could find other sources for their  manufacturing  needs.  Many of
these third parties and customers  have greater  financial,  technical and human
resources  than  Hybridon.  Key  competitive  factors will include the price and
quality of the products as well as manufacturing  capacity and ability to comply
with  specifications  and to fulfill  orders on a timely basis.  Hybridon may be
required to reduce the cost of its product  offerings to meet  competition.  See
"Management's  Discussion  And  Analysis Of Financial  Condition  And Results Of
Operations -- Risk Factors -- Hybridon Faces Intense Competition, And Hybridon's
Products Could Be Rendered Obsolete; Many Of Hybridon's Competitors Have Greater
Resources And Experience Than Hybridon."


EMPLOYEES

        As of March 31, 1999,  Hybridon  employed 51 individuals  full-time,  of
whom 20 held  advanced  degrees.  Nineteen  of these  employees  are  engaged in
research and development activities and eight are employed in finance, corporate
development  and legal  and  general  administrative  activities.  In  addition,
twenty-four  of these  employees are employees of HSP, of whom five are employed
in quality control.  Many of Hybridon's  management and  professional  employees
have had prior experience with pharmaceutical, biotechnology or medical products
companies.  None of Hybridon's  employees is covered by a collective  bargaining
agreement, and management considers relations with its employees to be good.


ITEM 2. PROPERTIES

        Hybridon   leases  its  36,000   square   foot   facility   in  Milford,
Massachusetts  under a lease which expires in 2004. The term of the lease may be
extended at Hybridon's option for two additional five-year terms.



                                       21

<PAGE>

        In addition, Hybridon leases supplemental laboratory space in Cambridge,
Massachusetts  comprising  approximately  26,000 square feet for a term expiring
April 30, 2007 at an annual rent of approximately $23 per square foot.  Hybridon
is currently  subleasing  approximately 20,000 square feet of this facility to a
third party under a sublease expiring September 30, 2000.


ITEM 3. LEGAL PROCEEDINGS

               Hybridon is not a party to any litigation  that it believes could
have a material adverse effect on Hybridon or its business.


ITEM 4. SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS

               No matters were  submitted  to a vote of security  holders in the
quarter ended December 31, 1998.


EXECUTIVE OFFICERS AND SIGNIFICANT EMPLOYEES OF THE COMPANY

        The executive  officers and  significant  employees of the Company as of
March 31, 1999 are as follows:

EXECUTIVE OFFICERS

<TABLE>
<CAPTION>

        NAME                            AGE        POSITION
        ----                            ---        --------

<S>                                     <C>        <C>    

E. Andrews Grinstead, III.............  53         Chairman of Board of  Directors, President and
                                                   Chief Executive Officer
Sudhir Agrawal, D. Phil...............  45         Senior Vice President of Discovery, Chief
                                                   Scientific Officer and Director





                                       22

<PAGE>

SIGNIFICANT EMPLOYEES

NAME                                    AGE        POSITION
- ----                                    ---        --------

Robert G. Andersen....................  48         Vice  President of  Operations  and Planning and
                                                   Treasurer
Judith Marquis, Ph.D, D.A, B.T........  52         Vice President of Pre-Clinical Development
R. Russell Martin, M.D. ..............  63         Vice President of Drug Development
Jin-Yan Tang, Ph.D. ..................  55         Vice President of Production
Cheryl M. Northrup....................  42         Vice President and General Counsel

</TABLE>

        Mr. Grinstead joined the Company in June 1991 and was appointed Chairman
of the Board and Chief Executive Officer in August 1991 and President in January
1993. He has served on the Board of Directors since June 1991.  Prior to joining
the Company,  Mr.  Grinstead  served as Managing  Director and Group Head of the
life sciences group at Paine Webber,  Incorporated,  an investment banking firm,
from 1987 to October 1990; Managing Director and Group Head of the life sciences
group at Drexel Burnham Lambert,  Inc., an investment banking firm, from 1986 to
1987; and Vice President at Kidder,  Peabody & Co.  Incorporated,  an investment
banking firm, from 1984 to 1986, where he developed the life sciences  corporate
finance  specialty  group.  Mr. Grinstead served in a variety of operational and
executive  positions with Eli Lilly and Company ("Eli Lilly"),  an international
pharmaceutical  company,  from 1976 to 1984, most recently as General Manager of
Venezuelan  Pharmaceutical,  Animal Health and Agricultural  Chemical Operations
and  at  Lilly  Corporate  Staff  as  Administrator,   Strategic   Planning  and
Acquisitions.  From 1991  until its merger  with  another  company in 1998,  Mr.
Grinstead served as a director of EcoScience  Corporation,  a development  stage
company engaged in the development of  biopesticides,  and has served since 1991
as a director of Pharmos Corporation, a development stage company engaged in the
development of novel  pharmaceutical  compounds and drug delivery  systems.  Mr.
Grinstead also serves as a director of Meridian  Medical  Technologies,  Inc., a
pharmaceutical  and medical device company.  Mr.  Grinstead was appointed to The
President's  Council of the National  Academy of Sciences  and the  Institute of
Medicine in January 1992 and the Board of the  Massachusetts  Biotech Council in
1997.  Since 1994, Mr. Grinstead has served as a member of the Board of Trustees
of the Albert B. Sabin Vaccine Foundation,  a charitable foundation dedicated to
disease prevention. Mr. Grinstead received an A.B. from Harvard College in 1967,
a J.D. from the University of Virginia School of Law in 1974 and an M.B.A.  from
the Harvard Graduate School of Business Administration in 1976.

        Dr.  Agrawal joined the Company in February 1990 and served as Principal
Research  Scientist  from February 1990 to January 1993 and as Vice President of
Discovery  from  December  1991 to January 1993 prior to being  appointed  Chief
Scientific  Officer in January  1993 and Senior Vice  President  of Discovery in
March 1994. He has served on the Board of



                                       23

<PAGE>

Directors since March 1993. Prior to joining the Company,  Dr. Agrawal served as
a Foundation  Scholar at the Worcester  Foundation  from 1987 through 1991.  Dr.
Agrawal  served as a  Research  Associate  at  Research  Council  Laboratory  of
Molecular Biology in Cambridge,  England,  from 1985 to 1986, studying synthetic
oligonucleotides.  Dr. Agrawal received a B.Sc. in chemistry, botany and zoology
in 1973,  an M.Sc.  in organic  chemistry in 1975 and a D. Phil. in chemistry in
1980 from Allahabad University in India.

        Mr.  Andersen  joined the Company and was  appointed  Vice  President of
Systems Engineering and Management Information Systems in November 1996 prior to
being  appointed Vice President of Operations and Planning in 1997 and Treasurer
of the Company in January  1998.  Prior to joining  the  Company,  Mr.  Andersen
served in a variety of positions at Digital  Equipment  Corporation,  a computer
company,  from 1986 to 1996,  most  recently  as Group  Manager  of the  Applied
Objects Group.  From 1978 to 1986, Mr. Andersen served in a variety of positions
at  United  Technologies  Corporation,  an  aviation  technology  company,  most
recently as Director of Quality.  Mr. Andersen received his B.E.E. in Electrical
Engineering  from  The  City  College  of New  York  in  1972  and a  M.S.  from
Northeastern University in 1978.

        Dr. Martin  joined the Company and served as Vice  President of Clinical
Research  from  April  1994 to  February  1997  prior  to being  appointed  Vice
President of Drug  Development in February  1997.  Prior to joining the Company,
Dr. Martin served in a variety of positions at Bristol Myers Squibb from 1983 to
1994,  most  recently  as  Vice  President  of  Clinical  Research   (Infectious
Diseases).  During such period, he served as an Adjunct  Associate  Professor of
Medicine and Associate  Clinical Professor at Yale University School of medicine
from 1987 to 1994,  Clinical  Professor at University of  Connecticut  School of
Medicine from 1986 to 1993 and Adjunct  Professor of Medicine at Baylor  College
of Medicine from 1993 to 1994. Prior to joining Bristol Myers Squibb, Dr. Martin
served as Professor of Medicine,  Microbiology  and Immunology at Baylor College
from 1975 to 1983.  Dr.  Martin  received an A.B. in American  studies from Yale
University in 1956 and an M.D. from the Medical College of Georgia in 1960.

        Dr. Marquis joined the Company in April, 1995, and served as Director of
Drug Safety Evaluation until January, 1998 when she was appointed Vice President
of Preclinical Development.  Prior to joining the Company, Dr. Marquis served as
Director of  Preclinical  Development at Procept,  Inc.,  from 1993 to 1995, and
Director of Life Sciences Research at Arthur D. Little, Inc., from 1989 to 1993.
Prior to joining the  pharmaceutical  industry,  Dr.  Marquis  spent 16 years in
medical  research and  education  at Tufts  University  School of Medicine.  Dr.
Marquis received a B.S. in Biology from Trinity College of Vermont in 1973 and a
Ph.D. in physiology  and  biophysics  from the  University of Vermont  School of
Medicine.  She is board  certified in toxicology  and a former  president of the
American Board of Toxicology.




                                       24

<PAGE>

         Ms.  Northrup  joined  the  Company  in  1997  and was  appointed  Vice
President and General  Counsel in June 1998.  Ms.  Northrup  served as Corporate
Counsel  to  ImmuLogic  Pharmaceutical  Corporation  from  1996 to 1997 and as a
Director of the Wallace Law Registry from 1994 to 1996. Ms. Northrup also served
as Director of Legal  Services of the Boston Five Cents  Savings  Bank from 1992
until 1994 and as Associate  General Counsel to American  Finance Group in 1990.
Prior to joining American Finance Group, Ms. Northrup was an Associate from 1981
to 1990 and a  Partner  from  1990 to 1991 of  Peabody  &  Brown,  a law firm in
Boston, Massachusetts.  Ms. Northrup received her A.B. degree from Smith College
in 1978 and a J.D. degree from Boston College Law School in 1981.

         Dr.  Tang  joined the  Company  in 1991 and  served as Senior  Research
Scientist from 1991 to 1993, Director of Oligonucleotide  Chemistry from 1993 to
1994 and Executive  Director of Process  Chemistry from 1994 to April 1995 prior
to being  appointed  Vice  President of Process  Development  in April 1995.  In
November of 1997, Dr. Tang was appointed Vice President of Production.  Prior to
joining  the  Company,  Dr. Tang  served as a Visiting  Fellow at the  Worcester
Foundation  from 1988 to 1991.  He also  served as a Visiting  Professor  at the
University of Colorado in 1988.  Dr. Tang received a B.S. in  biochemistry  from
Shanghai  University  of Sciences and  Technology  in 1965 and a Ph.D.  from the
Shanghai Institute of Biochemistry in 1978.





                                       25

<PAGE>

                                     PART II


ITEM 5. MARKET FOR REGISTRANT'S COMMON EQUITY AND RELATED
        STOCKHOLDER MATTERS


(a)     Market Information
        ------------------

        From January 24, 1996 until  December 2, 1997,  Hybridon's  Common Stock
was traded on the Nasdaq  National  Market  under the  symbol  "HYBN."  Prior to
January 24, 1996, there was no established  public trading market for Hybridon's
Common Stock.

        On December  2, 1997,  Hybridon's  Common  Stock was  delisted  from the
Nasdaq  National  Market and began being quoted on the NASD OTC Bulletin  Board.
Prices reflected on the NASD OTC Bulletin Board may reflect inter-dealer prices,
without  retail  mark-up,  mark-downs  or  commissions  and may not  necessarily
represent actual transactions.

        On December 10, 1997  Hybridon  effected a  one-for-five  reverse  stock
split of its Common  Stock.  As a result of the reverse  stock split,  each five
shares of  Common  Stock was  automatically  converted  into one share of Common
Stock, with cash paid in lieu of any fractional shares.

        The  following  table sets forth for the periods  indicated the high and
low sales  prices per share of the Common  Stock during each of the quarters set
forth below as reported on the Nasdaq  National Market and the NASD OTC Bulletin
Board since  January 24,  1996 and as  adjusted  to reflect  the  December  1997
reverse stock split.

<TABLE>
<CAPTION>

                                                   HIGH             LOW
                                                   ----             ---
<S>                                               <C>               <C>    

1996
- ----

First Quarter (from January 24, 1996)........      $71.250         $43.750
Second Quarter...............................       59.375          25.625
Third Quarter................................       59.375          33.125
Fourth Quarter...............................       43.125          26.250

1997
- ----

First Quarter................................      $43.125         $28.125
Second Quarter...............................       35.625          25.000
Third Quarter................................       28.125           7.500
Fourth Quarter...............................        4.859           2.609




                                       26

<PAGE>

1998
- ----

First Quarter................................        3.359           1.000
Second Quarter...............................        2.75            1.609
Third Quarter................................        2.516           1.125
Fourth Quarter...............................        3.25            1.125

1999
- ----

First Quarter................................       1.953             1.000

</TABLE>

        The  reported  closing  bid  price of the  Common  Stock on the NASD OTC
Bulletin Board on April 13, 1999 was $1.1875 per share.

(b)     Holders
        -------

        The number of Common Stockholders of record on April 13, 1999 was 351.

(c)     Dividends
        ---------

        The dividend rate of Hybridon's  Series A  convertible  preferred  stock
(the "Series A Preferred  Stock") is 6.5% per annum,  payable  semi-annually  in
arrears.  These dividends may be paid either in cash or in additional  shares of
Series A Preferred Stock, at the discretion of Hybridon.

        Hybridon has never  declared or paid cash dividends on its capital stock
and  does  not  expect  to pay any  dividends  on its  Common  Stock or any cash
dividends  on the  Series A  Preferred  Stock  in the  foreseeable  future.  The
Indenture under which Hybridon issued its 9% Convertible Subordinated Notes (the
"9% Notes") on April 2, 1997 limits Hybridon's  ability to pay dividends or make
other distributions on its Common Stock or to pay cash dividends on the Series A
Preferred  Stock. As of December  31,1998,  $1.3 million in aggregate  principal
amount of the 9% Notes remained outstanding.

        In addition, Hybridon is currently prohibited from paying cash dividends
under a $6,000,000  secured loan, which is owned by affiliates of two members of
Hybridon's  Board of  Directors.  See Note  7(b) to the  Consolidated  Financial
Statements.

(d)     Recent Sales of Unregistered Securities
        ---------------------------------------

        During the quarterly period ended December 31, 1998, the Company did not
sell any securities  that were not registered  under the Securities Act of 1933,
as amended.





                                       27

<PAGE>



ITEM 6. SELECTED FINANCIAL DATA

The selected financial data presented below have been derived from the Company's
Consolidated Financial Statements that have been audited by Arthur Andersen LLP,
independent  public   accountants.   This  financial  data  should  be  read  in
conjunction with the Management's Discussion and Analysis of Financial Condition
and Results of Operations,  the Consolidated  Financial Statements and the Notes
thereto and the other financial  information  appearing elsewhere in this Annual
Report on Form 10-K.

<TABLE>
<CAPTION>


                                                                        Years Ended December 31,
                                                 -----------------------------------------------------------------------
                                                          1994          1995           1996          1997          1998
                                                          ----          ----           ----          ----          ----
                                                                 (In thousands, except per share data)

<S>                                                   <C>           <C>            <C>            <C>          <C>   
Statement of Operations Data:
Revenues
     Research and development...................       $ 1,032       $ 1,186        $ 1,419         $ 945       $ 1,100
     Product and service revenue................            --            --          1,080         1,877         3,254
     Royalty income.............................            --            --             62            48            --
     Interest income............................           135           219          1,447         1,079           148
                                                       -------       -------        -------       -------       -------
                                                         1,167         1,405          4,008         3,949         4,502
Operating Expenses
     Research and development...................        20,024        29,685         39,390        46,828        20,977
     General and administrative.................         6,678         6,094         11,347        11,027         6,573
     Interest...................................            69           173            124         4,536         2,932
     Restructuring..............................            --            --             --        11,020            --
                                                       -------       -------        -------       -------       -------

          Total operating expenses..............        26,771        35,952         50,861        73,410        30,482
                                                       -------       -------        -------       -------       -------
Loss from operations............................      (25,604)      (34,547)       (46,853)      (69,461)      (25,980)
Extraordinary item:
     Gain on exchange of 9% convertible                     --            --             --            --         8,877
     subordinated notes payable.................       -------       -------        -------       -------       -------

Net Loss........................................      (25,604)      (34,547)       (46,853)      (69,461)      (17,104)
Accretion of preferred stock dividends..........            --            --             --            --         2,689
                                                       -------       -------        -------       -------       -------
Net loss to common stockholders.................     $(25,604)     $(34,547)      $(46,853)     $(69,461)     $(19,793)
                                                      ========      ========       ========      ========      ========

Basic and Diluted net loss per common share:
     Loss per share before extraordinary item...       $(70.77)      $(94.70)     $ (10.24)     $ (13.76)     $  (2.19)
     Extraordinary Item.........................             -             -             -              -          0.75
                                                       -------       -------        -------       -------       -------
     Net loss per share.........................        (70.77)       (94.70)       (10.24)       (13.76)        (1.44)

     Accretion of preferred stock dividends.....             -             -              -             -         (.23)
                                                       -------       -------        -------       -------       -------
     Net loss per share applicable to common
     shareholders...............................      $ (70.77)     $ (94.70)    $  (10.24)     $ (13.76)     $  (1.67)
                                                      ========      ========     ==========     =========     =========
Shares Used in Computing Basic and Diluted Net
Loss per Common Share...........................          362            365          4,576         5,050        11,859
                                                      ========      ========     ==========     =========     =========

Balance Sheet Data:
Cash, cash equivalents and short-term                   
investments.....................................        $3,396        $5,284       $ 16,419         2,202         5,608
Working capital (deficit).......................       (1,713)           210          8,891      (24,100)       (5,614)
Total assets....................................        11,989        19,618         41,537        35,072        16,536
Long-term debt, net of current portion..........         1,522         1,145          9,032         3,282         6,473
9% Convertible Subordinated
Notes Payable...................................            --            --             --        50,000         1,306
Accumulated Deficit                                   (67,794)     (102,341)      (149,194)     (218,655)     (238,448)
Total stockholders' equity (deficit)............         4,774        12,447         22,855      (46,048)         2,249

</TABLE>




                                       28

<PAGE>



ITEM 7. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL
        CONDITION AND RESULTS OF OPERATIONS

GENERAL

        Hybridon  is  engaged  in  the  discovery  and  development  of  genetic
medicines  based on  antisense  technology.  Hybridon  commenced  operations  in
February  1990 and since that time has been  engaged  primarily  in research and
development  efforts,  developing its  manufacturing  capabilities,  and raising
capital. In order to commercialize its therapeutic products,  Hybridon will need
to address a number of  technological  challenges and comply with  comprehensive
regulatory  requirements.  All  revenues  received by Hybridon to date have been
derived from collaborative  agreements,  interest on invested funds and revenues
from the custom contract  manufacturing of synthetic DNA and reagent products by
HSP.

        Hybridon has very limited cash resources and substantial  obligations to
lenders,  its real estate  landlords,  trade creditors,  and others.  Hybridon's
ability to continue  operations  in 1999 depends on its success in obtaining new
funds. If Hybridon is unable to obtain substantial additional new funding by the
end of May 1999, it will be required to terminate its  operations or seek relief
under applicable  bankruptcy laws.  Hybridon is currently seeking debt or equity
financing in an amount  sufficient to support its operations  through the end of
1999, and in connection  therewith,  is in negotiations  with several parties to
obtain such financing.

        In the Report of Independent  Public Accountants set forth in Appendix A
attached to this Annual Report on Form 10-K,  Arthur  Andersen  LLP,  Hybridon's
independent  public  accountants,  states that there is substantial  doubt about
Hybridon's ability to continue as a going concern.

        Hybridon has incurred  cumulative losses from inception through December
31, 1998 of approximately  $238.4 million.  Hybridon implemented a restructuring
plan  in the  second  half  of  1997,  which  significantly  reduced  Hybridon's
operating expenses in 1998 from 1997 levels. However,  Hybridon expects that its
research and  development  expenses will be significant in 1999 and future years
as it pursues  its core drug  development  programs  and  expects to continue to
incur operating losses and have significant  capital  requirements  that it will
not be able to satisfy with internally generated funds.

        This Annual Report on Form 10-K contains forward-looking statements. For
this purpose,  any statements  herein that are not statements of historical fact
may  be  deemed  to  be  forward-looking  statements.  For  example,  the  words
"believes,"  "anticipates,"  "plans,"  "expects"  and  similar  expressions  are
intended to identify forward-looking statements. Such forward-looking statements
are based on  management's  current  expectations  and involve known and unknown
risks,  uncertainties,  and other  factors  which may cause the actual  results,
performance  or  achievements  of Hybridon to be materially  different  from any
future  results,  performance,  or  achievements  expressed  or  implied by such
forward-looking  statements.  There are a number of important factors that could
cause  Hybridon's  actual results to differ  materially  from those indicated by
such  forward-looking  statements.  These factors include,  without  limitation,
those set forth below under the caption "Risk Factors."




                                       29

<PAGE>

RESTRUCTURING PLAN

        During the second half of 1997,  Hybridon  implemented  a  restructuring
plan to reduce  expenditures on a phased basis in an effort to conserve its cash
resources.  As part of this plan, in addition to terminating  the development of
GEM 91, Hybridon  reduced or suspended  programs  unrelated to its core advanced
chemistry antisense drug development  programs.  In addition,  in 1997, Hybridon
terminated the employment of a substantial  number of employees at its Cambridge
and  Milford,  Massachusetts  and Paris,  France  facilities  and  substantially
reduced operations at its Paris, France office. In December 1999, Hybridon began
the final process of terminating all operations in Europe.

        In 1997  Hybridon  subleased  a  portion  of each of its  facilities  in
Cambridge,   Massachusetts  (including  a  substantial  portion  of  its  former
headquarters). In June 1998, Hybridon relocated its headquarters from Cambridge,
Massachusetts to its facility in Milford,  Massachusetts  and subsequently  sold
its interest in Charles  River  Building  Limited  Partnership,  which owned the
former  Cambridge  headquarters.  In connection  with this  transaction  and the
termination of the Cambridge lease in 1998, the Company  received  $6,163,000 in
cash,  which  included the return of a portion of its  security  deposit for its
Cambridge  headquarters and the  reclassification on the Company's balance sheet
of $660,000 from  restricted  cash to cash and cash  equivalents.  The Cambridge
facility was re-leased in September 1998 to a third party, subject to a sublease
to a  portion  of the  premises.  As a result  of these  actions,  Hybridon  was
relieved  of its  substantial  lease  obligations  for the  Cambridge  facility,
subject to a continuing  liability  for any  defaults  which may arise under the
sublease.

RESULTS OF OPERATIONS

Years ended December 31, 1996, 1997 and 1998

Revenues

        Hybridon  had total  revenues of $4.0  million in 1996,  $3.9 million in
1997, and $4.5 million in 1998.  During 1996, 1997 and 1998,  Hybridon  received
revenues  from research and  development  collaborations  of $1.4 million,  $0.9
million and $1.1 million,  respectively.  Research and development collaboration
revenues decreased in 1997 from 1996 because of the cancellation by Roche of its
collaboration with Hybridon and the resulting elimination of research funding by
Roche.  Research and development  collaboration  revenues increased in 1998 from
1997,  primarily due to Hybridon  receiving  certain  payments under its license
agreement with MethylGene, Inc.

        Product and service  revenues were $1.1 million in 1996, $1.9 million in
1997 and $3.3  million in 1998.  The  increase in revenues in 1997 over those in
1996 resulted from a full year of operations for HSP, which commenced operations
in the third quarter of 1996. As of December 31, 1998, HSP had a backlog of $0.9
million.  Hybridon  anticipates  filling this backlog in the first half of 1999.
The increase in revenues in 1998 was primarily the result of an expansion by HSP
in the customer base and increased sales to certain existing customers,  and was
also due in part to Hybridon  receiving  $0.4  million in service  revenue  from
MethylGene.




                                       30

<PAGE>

        Revenues from interest income were $1.4 million in 1996, $1.1 million in
1997 and $0.1  million in 1998.  The  decrease in  interest  income in 1997 from
1996, and in 1998 from 1997 was the result of lower cash balances  available for
investment each year.

Research and Development Expenses

        During 1996,  1997 and 1998,  Hybridon  expended  $39.4  million,  $46.8
million and $21.0 million, respectively, on research and development activities.

        The  increases  in research and  development  expenses in 1997 from 1996
reflected  increasing  expenses related  primarily to ongoing clinical trials of
Hybridon's  product  candidates,  including (a) clinical trials of two different
formulations of GEM 132, which were first initiated  during the third quarter of
1996 and the first  quarter of 1997,  (b) clinical  trials of GEM 92, which were
initiated in the third quarter of 1997 and (c) clinical  trials of GEM 91, which
were  initiated in France in October 1993 and in the U.S. in May 1994,  and were
terminated  in  July  1997.  Clinical  expenses  related  to  GEM  91  decreased
significantly   during  the  second  half  of  1997  after  Hybridon  terminated
development of this compound.  Research and development  expenses also increased
in 1997 over 1996 due to significant  increases in preclinical expenses incurred
to meet the  filing  requirements  to  initiate  clinical  trials of  Hybridon's
product candidates in the United States.

        The  decrease  in research  and  development  expenses in 1998  reflects
Hybridon's  restructuring  that  commenced  during the second half of 1997.  The
restructuring   included  the   discontinuation   of  operations  at  Hybridon's
facilities in Europe,  termination of the clinical development of GEM 91 and the
reduction  or  suspension  of selected  programs  unrelated to  Hybridon's  core
advanced  chemistry  antisense  drug  development   program.  The  restructuring
resulted in significant  reductions in employee-related  expenses,  clinical and
outside testing, consulting, materials and lab expenses.

        The  facilities  expense  related to the research and  development  area
increased  significantly  in 1997 as a result of the relocation of the corporate
offices to Cambridge,  Massachusetts  and decreased  significantly  in 1998 as a
result of the relocation in July 1998 from Cambridge to Milford,  Massachusetts.
Hybridon's  facility costs in 1998 related to research and development were also
reduced by the income  received  from  subleasing  its  underutilized  Cambridge
facilities.

        Research  and  development   salaries  and  related  costs  remained  at
approximately  the same level in 1997 as 1996  because of the costs  involved in
terminating  employees in 1997.  Research and  development  salaries and related
costs decreased in 1998 from 1997 due to the substantial reduction in the number
of employees engaged in research and development in 1998.

        Patent expenses also remained at approximately the same level in 1998 as
1997 and 1996,  as Hybridon  continued  to limit the scope of patent  protection
that it  sought as part of its  effort to  conserve  its cash  resources,  while
prosecuting and maintaining key patents and patent applications.




                                       31

<PAGE>

General and Administrative Expenses

        Hybridon incurred general and  administrative  expenses of $11.3 million
in 1996, $11.0 million in 1997 and $6.6 million in 1998.

        The  decrease in general and  administrative  expenses in 1998  resulted
primarily from Hybridon's restructuring program initiated during the second half
of 1997 and its  effect on  employee-related  and  consulting  expenses  and net
facilities costs.

        The facilities  expense related to the general and  administrative  area
increased  significantly  in 1997 over 1996 as a result of the relocation of the
corporate  offices  to  Cambridge,  Massachusetts.  However,  as a result of the
implementation  of the  restructuring  plan in the  second  half of  1997,  such
increase  was offset by  decreases  in general and  administrative  salaries and
related  costs and in  consulting  expenses  in the second  half of 1997,  which
carried over into 1998. Hybridon's facilities expense related to the general and
administrative  area  decreased  significantly  in  1998  as  a  result  of  its
relocation to Milford,  Massachusetts.  Facility costs in 1998 were also reduced
by the income  received  from  subleasing  underutilized  Cambridge  facilities.
General and  administrative  expenses  related to business  development,  public
relations  and legal  expenses  decreased  in 1998 from 1997,  but  remained  at
approximately the same level in 1997 as 1996.

Interest Expense

        Interest expense was $0.1 million in 1996, $4.5 million in 1997 and $2.9
million in 1998. The decrease in interest expense in 1998 is mainly attributable
to  the  exchange  of   approximately   $48.7  million  of  the  9%  Convertible
Subordinated  Notes ("the 9% Notes"),  issued in the second quarter of 1997, for
Series A Preferred Stock on May 5, 1998. In addition, the outstanding balance of
borrowings  to finance the purchase of property and equipment was reduced in May
1998, resulting in a reduction in interest expense.

        The increase in interest expense in 1997 from 1996 reflected an increase
in Hybridon's debt outstanding  associated with the issuance of the 9% Notes and
interest  incurred  on  borrowings  to finance  the  purchase  of  property  and
equipment.

Restructuring Charge

        As a part of its restructuring  plan, Hybridon recorded an $11.0 million
restructuring charge in 1997 to provide for (i) the termination costs of certain
research  programs  and  other  contracts,  (ii)  the  loss  of  certain  leased
facilities  (net of  sublease  income  and other  contracts),  (iii)  severance,
benefits and related costs for 95  terminated  employees and (iv) the write down
of assets to net realizable value.

Net Loss

        As a result of the above  factors,  Hybridon  incurred net losses before
extraordinary  items of $46.9  million in 1996,  $69.5 million in 1997 and $26.0
million  in 1998.  Hybridon  had  extraordinary  income of $8.9  million in 1998
resulting  from the  exchange  of 9% Notes for Series A  Preferred  Stock in the
second  quarter of 1998. In accordance  with  Statement of Financial  Accounting
("SFAS")   No.15,   Accounting  by  Debtors  and  Creditors  for  Troubled  Debt
Restructurings, the Company recorded an extraordinary gain of approximately $8.9



                                       32

<PAGE>

million  related  to  the  exchange.   The  extraordinary  gain  represents  the
difference  between the carrying value of the 9% Notes tendered for exchange and
the fair value of the Series A  Preferred  Stock  issued upon the  exchange,  as
determined  by the per share  sales  price of such stock sold in May 1998 in the
private  offering  described  below. As a result of this  transaction,  Hybridon
reduced its net loss before  preferred stock dividends to $17.1 million in 1998.
Hybridon  had an  accretion  of  preferred  stock  dividends  of $2.7 million at
December  31,  1998 to  reflect  the 1998  portion of  dividends  payable to the
holders of Series A  Preferred  Convertible  Stock,  resulting  in a net loss to
common stockholders of $19.8 million for 1998.


LIQUIDITY AND CAPITAL RESOURCES

General

        Since inception,  Hybridon has incurred  significant losses which it has
funded through the issuance of equity securities,  debt issuances, sales by HSP,
and through research and development collaborations and licensing arrangements.

        During the year ended December 31, 1998, Hybridon utilized approximately
$21.5  million to fund  operating  activities  and  approximately  $472,000  for
capital  expenditures.  The primary use of cash for operating  activities was to
fund  Hybridon's  loss  before  extraordinary  items of $26.0  million.  Capital
expenditures  during  1998  included  amounts  expended  for the  build-out  and
equipping  of  Hybridon's  corporate   headquarters  and  primary  research  and
development  laboratories  in its  leased  manufacturing  facility  in  Milford,
Massachusetts.  Hybridon  expects  to  purchase  a  minimal  amount  of  capital
equipment in 1999 as part of its effort to conserve cash resources.

Cash Resources

        Hybridon had cash and cash  equivalents  of $5.6 million at December 31,
1998. However,  since that date, Hybridon has expended the majority of such cash
resources and continues to have substantial  obligations to lenders, real estate
landlords, trade creditors and others. On March 30, 1999, Hybridon's obligations
included  $1.3 million  principal  amount of 9% Notes,  a $6.0 million loan with
Forum Capital Markets, LLC and others, as described below, $0.5 million of notes
payable  and  approximately  $2.4  million  of  accounts  payable.   Because  of
Hybridon's financial condition, many trade creditors are only willing to provide
Hybridon with products and services on a cash on delivery basis.

        Hybridon's ability to continue operations in 1999 depends on its success
in obtaining new funds in the immediate  future.  Hybridon is currently  seeking
debt or equity  financing  in an amount  sufficient  to support  its  operations
through the end of 1999, and in connection  therewith,  is in negotiations  with
several  parties to obtain such  financing.  However,  there can be no assurance
that Hybridon will obtain any funds or as to the timing thereof.  If the Company
is unable to obtain  substantial  additional new funding by the end of May 1999,
Hybridon  may be required to further  curtail  significantly  one or more of its
core  drug  development   programs,   obtain  funds  through  arrangements  with
collaborative  partners or others that may  require it to  relinquish  rights to
certain of its  technologies,  product  candidates  or  products  which it would
otherwise  pursue  on its  own or  terminate  operations  or seek  relief  under
applicable  bankruptcy  laws. It is also possible that Hybridon's  creditors may
seek to commence involuntary bankruptcy proceedings against the Company.



                                       33

<PAGE>

        Even if Hybridon obtains sufficient cash to fund its operations in 1999,
it will be required  to raise  substantial  additional  funds  through  external
sources,  including  through  collaborative  relationships and public or private
financings,  to support its  operations  beyond  1999.  Except for  research and
development  funding from Searle under its  collaborative  agreement with Searle
(which is subject to early termination in certain  circumstances),  Hybridon has
no committed  external sources of capital,  and, as discussed above,  expects no
product  revenues for several years from sales of the therapeutic  products that
it is developing (as opposed to sales of DNA products and reagents  manufactured
and sold by HSP).

        No  assurance  can be given that  additional  funds will be available to
fund  operations  for the balance of 1999 or in future years,  or, if available,
that such funds will be available on acceptable  terms. If additional  funds are
raised  by  issuing  equity  securities,   further  dilution  to  then  existing
stockholders  will  result.  Additionally,  the  terms  of any  such  additional
financing  may  adversely  affect  the  holdings  or  rights  of  then  existing
stockholders.

        Hybridon's  future  capital  requirements  will depend on many  factors,
including  continued  scientific  progress in its research,  drug  discovery and
development programs, the magnitude of these programs, progress with preclinical
and clinical trials,  sales of DNA products and reagents to third parties by HSP
and the  margins  on such  sales,  the  time and  costs  involved  in  obtaining
regulatory  approvals,  the costs involved in filing,  prosecuting and enforcing
patent  claims,  competing  technological  and market  developments,  Hybridon's
ability  to  establish  and  maintain   collaborative  academic  and  commercial
research,  development  and  marketing  relationships,  its  ability  to  obtain
third-party financing for leasehold  improvements and other capital expenditures
and the costs of  manufacturing  scale-up and  commercialization  activities and
arrangements.

1998 FINANCING ACTIVITIES

        On February 6, 1998,  Hybridon  commenced an offer to the holders of the
9% Notes to  exchange  the 9% Notes for  Series A  Preferred  Stock and  certain
warrants of  Hybridon.  On May 5, 1998,  noteholders  holding  $48.7  million of
principal  and $2.4 million of accrued  interest  tendered  such  principal  and
accrued  interest to Hybridon for 510,505 shares of Series A Preferred Stock and
warrants to purchase  3,002,958 shares of common stock with an exercise price of
$4.25 per share.

        On  May 5,  1998,  Hybridon  completed  a  private  offering  of  equity
securities raising total gross proceeds of approximately  $26.7 million from the
issuance  of  9,597,476  shares  of  common  stock,  114,285  shares of Series A
Preferred  Stock and  warrants to purchase  3,329,486  shares of common stock at
$2.40 per share. The gross proceeds include the conversion of approximately $5.9
million of accounts  payable,  capital lease  obligations and other  obligations
into common stock. Hybridon incurred approximately $1.6 million of cash expenses
related to the private  offering and issued  597,699  shares of common stock and
warrants to purchase  1,720,825 shares of common stock at $2.40 per share to the
placement  agents.  In addition,  Hybridon is  obligated to issue an  additional
300,000 shares in connection with this  transaction.  For more information about
this transaction, see Note 15(c) of the Notes to Consolidated Statements.





                                       34

<PAGE>

Credit Facility

        In December  1996,  Hybridon  entered into a five year  $7,500,000  note
payable  with a bank.  The  note  contained  certain  financial  covenants  that
required  Hybridon to maintain minimum tangible net worth and minimum  liquidity
and  prohibited  the  payment  of  dividends.  The note was  payable in 59 equal
installments of $62,500 commencing on February 1, 1997 with a balloon payment of
the then remaining outstanding principal balance due on January 1, 2002. Because
Hybridon was required to make certain  prepayments of principal during 1998, the
outstanding principal balance of the loan at November 16, 1998 was approximately
$2.8 million.  The lender has granted  Hybridon a waiver of compliance  with the
minimum  tangible net worth  requirement at December 31, 1998 and March 31, 1999
and the minimum liquidity requirement at April 15, 1999.

        Effective  November 20, 1998, Forum Capital  Markets,  LLC ("Forum") and
certain investors associated with Pecks Management Partners Ltd. ("Pecks"; Forum
and Pecks  collectively,  the "Lender")  purchased the loan from the bank. Forum
and Pecks are  affiliates  of two members of Hybridon's  Board of Directors.  In
connection  with this  purchase,  the Lender lent an additional  $3.2 million to
Hybridon  so as to  increase  the  outstanding  principal  amount of the note to
$6,000,000. In addition, the terms of the note payable were amended as follows:

        (i)    the maturity was extended to November 30, 2003;

       (ii)    the interest rate was decreased to 8%;

      (iii)    interest is payable monthly in arrears, with the principal due in
               full at maturity;

       (iv)    the note payable is convertible, at the Lender's option, in whole
               or in  part,  into  shares  of  common  stock  of  Hybridon  at a
               conversion price equal to $2.40 a share;

        (v)    the threshold of the minimum liquidity  covenant was reduced from
               $4,000,000 to $2,000,000; and

       (vi)    the note payable may not be prepaid,  in whole or in part, at any
               time prior to December 1, 2000.

The other terms of the note payable were unchanged.

For further information about this loan, see Note 7 of the Notes to Consolidated
Financial Statements.

Facility Leases

        As of December 31, 1998, Hybridon has future operating lease commitments
of approximately $7.7 million through 2007 for its existing leases.

Net Operating Loss Carryforwards

        As of December 31, 1998,  Hybridon had approximately  $220.0 million and
$3.9 million of net operating loss and tax credit  carryforwards,  respectively.
The Tax Reform Act of 1986 (the "Tax Act") contains certain  provisions that may
limit  Hybridon's   ability  to  utilize  net  operating  loss  and  tax  credit
carryforwards  in any given year if certain events occur,  including  cumulative
changes  in  ownership  interests  in  excess of 50% over a  three-year  period.
Hybridon has completed  several  financings  since the effective date of the Tax
Act,



                                       35

<PAGE>

which, as of December 31, 1998, have resulted in ownership  changes in excess of
50%,  as defined  under the Tax Act and which will limit  Hybridon's  ability to
utilize its net operating loss carryforwards.

YEAR 2000

        As has been widely publicized, many computer systems and microprocessors
are not  programmed  to  accommodate  dates  beyond  the year  1999.  Hybridon's
exposure to this year 2000 ("Y2K")  problem comes not only from its own internal
computer   systems   and   microprocessors,   but  also  from  the  systems  and
microprocessors  of its key suppliers,  including  utility companies and payroll
services.

        Hybridon believes that all of its internal systems will be Y2K compliant
by the end of the third quarter of 1999. Hybridon is currently evaluating all of
its internal computer systems and  microprocessors  in light of the Y2K problem.
As part of this  process,  Hybridon has  conducted an inventory of its automated
instruments  and  other  computerized  equipment  and is  contacting  applicable
vendors for information regarding Y2K compliance.  Hybridon will then upgrade or
otherwise  modify its  internal  computer  systems and  microprocessors,  to the
extent   necessary.   Testing  of  all  its   internal   computer   systems  and
microprocessors  was completed in the first  quarter of 1999.  Hybridon does not
expect the cost of bringing all Hybridon's systems and microprocessors  into Y2K
compliance will be material. Approximately 50% of Hybridon's systems either have
been found compliant or have already been brought into compliance.

        Hybridon's  Y2K  compliance  efforts are in  addition  to other  planned
information technology ("IT") projects.  While these efforts have caused and may
continue to cause delays in other IT projects, Hybridon does not expect that any
of these delays will have a significant  effect on  Hybridon's  business or that
any of Hybridon's other IT projects will be canceled or postponed to pay for the
Y2K upgrades.

        With regard to potential supplier Y2K problems,  Hybridon has compiled a
list  of  its  critical  suppliers,  and  has  sent  and  received  back  a  Y2K
questionnaire from each of them in order to permit Hybridon to ascertain the Y2K
compliance  status of each.  Hybridon has not yet uncovered any key supplier Y2K
problems that could have a material effect on its business. If through continued
monitoring of these suppliers Hybridon becomes aware of any such problems and is
not satisfied that those problems are being adequately  addressed,  it will take
appropriate steps to find alternative suppliers.

        It has been  acknowledged by governmental  authorities that Y2K problems
have the potential to disrupt global economies,  that no business is immune from
the potentially  far-reaching effects of Y2K problems,  and that it is difficult
to  predict  with   certainty   what  will  happen  after   December  31,  1999.
Consequently,  it is possible that Y2K problems  will have a material  effect on
Hybridon's  business even if Hybridon takes all  appropriate  measures to ensure
that it and its key suppliers are Y2K compliant.

        It is  possible  that  the  conclusions  reached  by  Hybridon  from its
analysis to date will change,  which could cause  Hybridon's  Y2K cost estimates
and target completion dates to change.





                                       36

<PAGE>

RISK FACTORS

        The  following  important  factors,  among  others,  could cause  actual
results to differ materially from those contained in forward-looking  statements
made in this Annual  Report on Form 10-K and  presented  elsewhere by management
from time to time.


Hybridon May Never Generate Revenues From Sales Of Its Drugs

        Hybridon's business is at an early stage of development, and has not yet
generated any revenues from the commercial sale of its drugs. Due to the various
risks  inherent in its business and  described in the  following  risk  factors,
Hybridon  may never  generate  revenues  from sale of its  drugs,  and may never
become  profitable.  See  "Management's  Discussion  And  Analysis Of  Financial
Condition And Results Of Operations -- Results Of Operations" and " -- Liquidity
And Capital Resources."

Hybridon Has A History Of Operating Losses, And Anticipates Future Losses

        Hybridon  has never  earned a profit and has  incurred  substantial  net
operating  losses.  These losses were caused by lack of revenues from drug sales
to offset research and development and administrative costs. Hybridon expects to
incur operating losses for at least the next several years, as it plans to spend
substantial amounts on research and development,  including  preclinical studies
and clinical trials, and, if it obtains necessary regulatory approvals, on sales
and marketing  efforts.  See "Management's  Discussion And Analysis Of Financial
Condition And Results Of Operations -- Results Of Operations" and " -- Liquidity
And Capital Resources."


Hybridon May Determine That One Or More Drugs In Development Are Commercially
Impractical And Cannot Be Sold Commercially

        Before a drug is sold commercially,  it must go through an expensive and
time-consuming  testing process.  Hybridon's drugs are at various stages in this
process, and Hybridon may at any stage determine that one or more of these drugs
cannot be successfully developed. A drug may, for instance, be ineffective, have
undesirable side effects, or demonstrate other therapeutic  characteristics that
prevent  or limit its  commercial  use,  or may prove too  costly to  produce in
commercial quantities. If Hybridon determines that a drug cannot be successfully
developed,  Hybridon  would not be able to generate  revenues  from sale of that
drug.


Seeking Regulatory Approval Of Drugs Is Time-Consuming And Expensive; Failure To
Obtain Approval Of A Drug Would Prevent Hybridon From Selling That Drug; Failure
To Comply With Ongoing Regulatory Requirements Could Cause Hybridon To Be
Subject To Penalties

        Hybridon is subject to  extensive  regulation  by numerous  governmental
authorities in the U.S. and abroad.  Obtaining regulatory approval of a drug can
take several  years  --exactly how long depends upon the type,  complexity,  and
novelty of the drug -- and is



                                       37

<PAGE>

typically very  expensive.  The  regulations  that Hybridon must comply with may
change, and may even become more burdensome to Hybridon.

        Even if Hybridon is  satisfied  that a drug is safe and  effective,  the
regulatory  authorities  may not agree,  as data from  preclinical  studies  and
clinical  trials can generally be interpreted in different  ways.  Hybridon will
need the approval of  regulatory  agencies in order to sell a drug.  If they are
unwilling to grant that approval, Hybridon will not be able to generate revenues
from sale of that drug.

        Approval  of  a  drug  does  not  end  the   involvement  of  regulatory
authorities. Hybridon and its approved drugs will be subject to continued review
and  periodic  inspection.  Approval  of a  Hybridon  drug  may  be  subject  to
restrictions  that limit how Hybridon may market that drug.  Restrictions may be
imposed on the price at which Hybridon may sell its drugs.  If Hybridon fails to
comply  with  any  regulations,  it may  be  subject  to  fines,  suspension  of
regulatory approvals, drug recalls, and other penalties.


Delays In Patient Enrollment Could Increase The Cost Or Duration Of Hybridon's
Clinical Studies

        Clinical trials are very costly and time-consuming. How quickly Hybridon
is able to complete a clinical study depends upon several factors, including the
size of the patient  population,  how easily patients can get to the site of the
clinical study, and the criteria for determining  which patients are eligible to
join the  study.  Delays in  patient  enrollment  could  delay  completion  of a
clinical study and increase its costs,  and could also delay the commercial sale
of the drug that is the subject of the clinical trial.


Hybridon  Must Secure  Additional  Funding To Avoid  Terminating  Operations  Or
Filing  For  Bankruptcy;  It May  Not Be Able To  Secure  Sufficient  Additional
Financing

        Hybridon has very limited cash resources and substantial  obligations to
lenders,  its real estate  landlords,  trade  creditors  and others.  Hybridon's
ability to continue  operations  in 1999 depends on its success in obtaining new
funds. If Hybridon is unable to obtain substantial additional new funding by the
end of May 1999,  it will be forced to terminate  its  operations or seek relief
under applicable  bankruptcy laws. See "Management's  Discussion And Analysis Of
Financial  Condition  And  Results  Of  Operations  --  General"  and  "--  Cash
Resources."

        In their report on Hybridon's  December 31, 1998  financial  statements,
Arthur Andersen LLP,  Hybridon's  independent  public  accountants,  states that
there is  substantial  doubt  about  Hybridon's  ability to  continue as a going
concern.

        Hybridon  anticipates  that, even if it obtains  sufficient cash to fund
its  operations  in 1999,  it will be required to raise  substantial  additional
funds through external sources,  including through  collaborative  relationships
and public or private financings,  to support Hybridon's operations beyond 1999.
If  adequate  funds are not  available,  Hybridon  may be forced to (1)  further
curtail significantly one or more of its research,  drug recovery or development
programs,  (2) obtain funds through arrangements with collaborative  partners or
others  that may  require  Hybridon  to  relinquish  rights  to  certain  of its
technologies, drug


                                       38


<PAGE>

candidates  or  drugs,  (3)  terminate  operations,  or (4)  seek  relief  under
applicable bankruptcy laws.


Additional Financing May Cause Stockholder Dilution

        If Hybridon raises  additional funds by issuing equity  securities,  the
ownership  interest  of existing  stockholders  will be  diluted.  In  addition,
Hybridon  may  grant  future  investors  rights  superior  to those of  existing
stockholders.


If Hybridon Defaults Under Its Loan, It Could Be Forced To Terminate  Operations
Or File For Bankruptcy

        Hybridon is a party to a substantial  loan.  The lenders may  accelerate
the repayment date of the loan in the event of default by Hybridon.  If Hybridon
does default on the loan,  and the lenders  accelerate  the repayment  date, the
lenders could foreclose on Hybridon's  assets,  and this could force Hybridon to
terminate  operations or seek relief under applicable  bankruptcy laws. Hybridon
cannot  guarantee  that it will  not  default  on the  loan.  See  "Management's
Discussion And Analysis Of Financial Condition And Results Of Operations -- 1998
Financing Activities."


The "Penny Stock" Rules Will Likely Have An Adverse Effect On Your Liquidity And
Hybridon's Ability To Raise Additional Capital

        Since the Common Stock is not listed on a national  securities  exchange
or on a qualified automated quotation system, it is subject to the "penny stock"
provisions of Rule 15g-9 under the Securities  Exchange Act of 1934, as amended,
which impose additional sales practice  requirements on broker-dealers that sell
such   securities.   Prior  to  any  transaction   covered  by  this  rule,  the
broker-dealer  must  receive  from  the  purchaser  a  written  consent  to  the
transaction, and must reasonably determine that transactions in penny stocks are
suitable for the purchaser,  and that the purchaser is capable of evaluating the
risks of transactions in penny stocks.  These  requirements  will likely have an
adverse effect on the market liquidity of Hybridon's  securities,  and therefore
on  Hybridon's  ability to raise funds,  the ability of  broker-dealers  to sell
Hybridon's  securities,  and the  ability  of  purchasers  to sell  any of their
Hybridon securities in the secondary market.


Hybridon May Be Unable To Obtain Or Enforce Patents; Its Patents May Not Provide
Adequate Protection

        Hybridon's  success  will depend to a large extent on its ability to (1)
obtain U.S. and foreign patent protection for drug candidates and processes, (2)
preserve trade secrets and (3) operate without infringing the proprietary rights
of third parties.  Legal standards  relating to the validity of patents covering
pharmaceutical  and  biotechnological  inventions  and the scope of claims  made
under such  patents are still  developing.  As a result,  Hybridon's  ability to
obtain and enforce  patents  that  protect its drugs is  uncertain  and involves
complex legal and factual questions.


                                       39


<PAGE>

        To obtain a patent on an  invention,  one must be the first to invent it
or the  first to file a patent  application  for it.  Hybridon  also  cannot  be
completely  sure that the inventors of subject matter covered by its patents and
patent  applications  were the  first to  invent,  or the  first to file  patent
applications for, those inventions.  Furthermore, that Hybridon owns or licenses
pending or future patent  applications does not mean that patents based on those
applications  will  ultimately  be issued.  Existing  or future  patents  may be
challenged,  infringed,  invalidated, found to be unenforceable, or circumvented
by others. Hybridon's rights under any issued patents may not provide sufficient
protection  against  competing  drugs or otherwise cover  commercially  valuable
drugs or processes. See "Business -- Patents, Trade Secrets and Licenses."


Hybridon  Could  Become  Involved  In   Time-Consuming   And  Expensive   Patent
Litigation; Adverse Decisions In Patent Litigation Could Cause Hybridon To Incur
Additional Costs And Experience Delays In Bringing New Drugs To Market

        The pharmaceutical and biotechnology  industries have been characterized
by time-consuming and extremely expensive litigation regarding patents and other
intellectual  property rights.  Hybridon may be required to commence,  or may be
made  a  party  to,  litigation  relating  to  the  scope  and  validity  of its
intellectual  property rights,  or the  intellectual  property rights of others.
Such litigation could result in adverse decisions regarding the patentability of
Hybridon's inventions and products, or the enforceability, validity, or scope of
protection offered by its patents. Such decisions could make Hybridon liable for
substantial  money damages or could bar Hybridon from the  manufacture,  use, or
sale of certain  products,  resulting in additional costs and delays in bringing
drugs to market.  Hybridon may not have  sufficient  resources to bring any such
proceedings to a successful conclusion.

        Hybridon also may be required to participate in interference proceedings
declared by the U.S.  Patent and  Trademark  Office (or similar  proceedings  in
foreign  countries) and in International  Trade Commission  proceedings aimed at
preventing  the  importing of drugs that would  compete  unfairly  with Hybridon
drugs. Such proceedings could cause Hybridon to incur considerable costs.

Hybridon's Trade Secrets And Other Unpatented Proprietary Information May Become
Available To Others

        Trade  secrets and other  unpatented  proprietary  information  plays an
important  role  in  Hybridon's   business.   Hybridon  seeks  to  protect  this
information,   in  part  by  means  of   confidentiality   agreements  with  its
collaborators,  employees,  and  consultants.  If any  of  these  agreements  is
breached,  Hybridon may be without  adequate  remedies.  Also,  Hybridon's trade
secrets may become  known or be  independently  developed by  competitors.  This
could have a material  adverse effect on Hybridon's  business,  and Hybridon may
need  to  engage  in  costly  and  time-consuming   litigation  to  protect  its
proprietary rights.


The Loss Of Key Members Of Management Could Be Damaging

        Hybridon  depends  on  the  principal  members  of  its  management  and
scientific staff, including E. Andrews Grinstead III, Hybridon's Chairman of the
Board, President and its Chief Executive Officer, and Sudhir Agrawal, Hybridon's
Senior Vice President of Discovery


                                       40


<PAGE>

and its  Chief  Scientific  Officer.  The loss of their  services  could  have a
material adverse effect on Hybridon.


Hybridon  May Not Be Able To Meet Its  Personnel  Needs;  This  Could  Result In
Delays Or Additional Costs

        From June 30,  1997,  to March 31,  1999,  the  number of  employees  of
Hybridon  decreased from 213 to 51. As a result,  Hybridon has lost  significant
expertise,  and must recruit and retain new scientific personnel to maintain its
current level of operations, while expansion would require a further increase in
scientific personnel. In addition,  expansion by Hybridon would likely result in
the  need  for  additional  management  personnel.  Hybridon  may not be able to
attract and retain  personnel on acceptable  terms,  given the  competition  for
experienced   scientists   and   management   among   numerous   pharmaceutical,
biotechnology and health care companies,  universities,  and non-profit research
institutions. The failure to recruit and retain personnel could result in delays
in commercializing drugs, and could cause Hybridon to incur additional costs.


Hybridon  Relies On  Relationships  With  Research  Institutions  And  Corporate
Partners,  And  Would  Be  Harmed  By A Lack Of,  Or The  Termination  Of,  Such
Relationships

        Hybridon's  success  will  depend in part on its  continued  ability  to
develop and maintain  relationships  with  independent  researchers  and leading
academic and research  institutions.  The competition for such  relationships is
intense, and Hybridon can give no assurances that it will be able to develop and
maintain such  relationships  on acceptable  terms.  Hybridon has entered into a
number of such collaborative  relationships relating to specific disease targets
and  other  research  activities  in  order to  augment  its  internal  research
capabilities  and to obtain access to  specialized  knowledge or expertise.  The
loss of any of these  collaborative  relationships could have a material adverse
effect on Hybridon's research and development program.

        Similarly,   strategic  alliances  with  corporate  partners,  primarily
pharmaceutical  and  biotechnology  companies,  may help  Hybridon  develop  and
commercialize  drugs.  Various  problems  can arise in  strategic  alliances.  A
partner  responsible  for conducting  clinical  trials and obtaining  regulatory
approval may fail to develop a  marketable  drug. A partner may decide to pursue
an alternative strategy or alternative partners. A partner that has been granted
marketing  rights for a certain drug within a geographic area may fail to market
the drug  successfully.  Consequently,  Hybridon's current strategic alliance or
those it enters  into in the future may not be  scientifically  or  commercially
successful.  Hybridon may not able to negotiate advantageous strategic alliances
in the future.  The absence of, or failure of,  strategic  alliances  could harm
Hybridon's efforts to develop and commercialize its drugs.


HSP's Results May Be Lower Than Currently Anticipated

        Through HSP, Hybridon manufactures oligonucleotide compounds for sale to
others.  The  results of HSP will  depend on the demand for and margins on these
drugs, which may be lower than Hybridon anticipates.  HSP's results will also be
affected by the price and availability of raw materials.


                                       41


<PAGE>

Hybridon Faces Intense Competition, And Hybridon's Products Could Be Rendered
Obsolete; Many Of Hybridon's Competitors Have Greater Resources And Experience
Than Hybridon

        Many companies are attempting to develop drugs similar to those Hybridon
proposes to develop.  Some of these  drugs are in clinical  trials,  and one has
received FDA approval and is being commercialized.  In addition, there are other
drugs  already  available  for  the  treatment  of  many  of the  diseases  that
Hybridon's  proposed  drugs  would  treat.  Any of these  drugs may  prove  more
effective than those that Hybridon proposes to develop, and may gain or maintain
greater market acceptance.

        Furthermore,  biotechnology and related pharmaceutical technologies have
undergone and continue to be subject to rapid and significant  change.  Hybridon
expects  that  the  technologies  associated  with  biotechnology  research  and
development will continue to develop rapidly.  Hybridon's  future will depend in
large part on its ability to compete  with these  technologies.  Any  compounds,
drugs or processes that Hybridon develops may become obsolete before it recovers
expenses incurred in developing those drugs.

        Many of Hybridon's  competitors have  substantially  greater  financial,
technical,  and human resources than Hybridon,  and have  significantly  greater
experience  than  Hybridon in  preclinical  studies,  clinical  trials,  seeking
regulatory approval of new drugs, and manufacturing and marketing new drugs.


Hybridon's Manufacturing Capability May Be Adversely Affected By Problems With
Suppliers

        Certain of the raw  materials  that  Hybridon  requires  to  manufacture
oligonucleotides  are  available  from only a few  suppliers,  namely those with
access to the  appropriate  patented  technology.  The  number of  suppliers  is
unlikely to increase in the near  future.  Hybridon may not be able to secure an
adequate  supply  of  these  materials  at an  acceptable  price.  Also,  due to
regulatory  restrictions  or other  problems,  Hybridon's  suppliers may fail to
provide materials of acceptable quality.


Hybridon's Lack Of Marketing Experience Could Adversely Affect Its Ability To
Commercialize Its Drugs

        Direct   marketing  of  any  of  its  proposed  drugs  would  require  a
substantial  marketing staff and sales force supported by a distribution system.
Given that Hybridon  currently has little  experience  in sales,  marketing,  or
distribution,  Hybridon might not be able to undertake  direct  marketing of its
drugs in a  cost-effective  manner.  The  alternative --  co-marketing  or other
licensing  arrangements  -- would allow Hybridon to avoid the  significant  cost
involved in direct marketing,  but would require Hybridon to rely on the efforts
of others.


                                       42


<PAGE>

Hybridon Could Be Subject To Product Liability Claims For Which It Is Not Fully
Insured

        Hybridon  risks being the target of product  liability  claims  alleging
that its drugs harm  subjects  or  patients.  Such  claims  could be asserted in
connection  with  Hybridon  drugs used in clinical  trials as well as those sold
commercially.  Hybridon is covered  against  such claims by a product  liability
insurance  policy  (subject  to  various  deductibles),  but such  policies  are
becoming increasingly expensive. Hybridon may not be able to maintain sufficient
coverage  to  protect  it  from  incurring  significant  losses  due to  product
liability claims.


Hybridon Uses Hazardous Materials, And Could Be Held Liable For Damages In The
Event Of Accidental Contamination Or Injury

        Hybridon's activities involve the controlled use of hazardous chemicals,
viruses, and radioactive  compounds.  Although Hybridon believes that its safety
procedures  for  handling  and  disposing  of such  materials  comply  with  the
standards  prescribed  by federal,  state,  and local  regulations,  the risk of
accidental contamination or injury cannot be completely eliminated. In the event
of such an accident, Hybridon could be held liable for any damages that result.


Restrictions  On Third-Party  Reimbursement  Could Adversely  Affect  Hybridon's
Ability To Commercialize Its Drugs

        Hybridon's  ability to commercialize  drugs  successfully will depend in
part on the extent to which  various  third  parties  are  willing to  reimburse
patients for the costs of Hybridon's drugs and related  treatments.  These third
parties  include  government  authorities,  private health  insurers,  and other
organizations, such as health maintenance organizations.  Third-party payors are
increasingly  challenging the prices charged for medical  products and services.
Accordingly,  if less costly  drugs are  available,  third-party  payors may not
authorize or may limit  reimbursement  for  Hybridon's  drugs,  even if they are
safer or more effective  than the  alternatives.  In addition,  the trend toward
managed  healthcare  and  government  insurance  programs  could result in lower
reimbursement and reduced demand for Hybridon's drugs. Cost containment measures
instituted  by  healthcare  providers  and any general  healthcare  reform could
affect  Hybridon's  ability to sell drugs and may have a material adverse effect
on  Hybridon.  Hybridon  may be forced to reduce its prices;  this would in turn
adversely affect profitability.

        Hybridon  cannot  predict  what  additional  legislation  or  regulation
relating to the health care industry or third-party  coverage and  reimbursement
may be enacted in the  future,  or what effect such  legislation  or  regulation
might have on its business. In particular,  Hybridon may be forced to reduce its
prices; this would in turn adversely affect profitability.


The Market Price Of Hybridon's Securities Is Likely To Be Volatile

        The market price of the  securities of  biotechnology  companies such as
Hybridon is highly volatile.  The market price of Hybridon's securities could be
influenced by the results of preclinical studies and clinical trials by Hybridon
or its competitors, fluctuations in


                                       43


<PAGE>

Hybridon's  operating  results,  announcements by Hybridon or its competitors of
technological  innovations or new commercial  therapeutic  products,  changes in
governmental  regulation,  developments in patent or other proprietary rights of
Hybridon or its competitors,  public concern as to the safety of drugs developed
by Hybridon, and general market conditions.


Hybridon Does Not Anticipate Paying Dividends On Common Stock In The Foreseeable
Future

        Hybridon has never paid any cash  dividends on the Common Stock and does
not anticipate paying any in the foreseeable future. Furthermore,  the Indenture
pursuant  to which the 9% Notes were  issued  limits  Hybridon's  ability to pay
dividends  or make other  distributions  on the Common  Stock,  and  Hybridon is
currently  prohibited under the terms of its $6,000,000 secured loan from paying
cash dividends. Whether Hybridon is ultimately able to pay cash dividends on the
Common Stock  depends on  Hybridon's  future  earnings,  operating and financial
condition, and capital requirements, and on general business conditions.


Hybridon's Ability To Utilize Its Net Operating Losses And Tax Credits Is Likely
To Be Severely Restricted

        Hybridon has substantial net operating loss and tax credit carryforwards
for federal income tax purposes.  These  carryforwards  will expire beginning on
December  31,  2005.  The Tax  Reform  Act of 1986  limits the annual use of net
operating loss and tax credit carryforwards following certain ownership changes.
The securities offerings conducted by Hybridon will severely restrict Hybridon's
ability to utilize its net  operating  losses and tax credits in any  particular
year.  Additionally,  because the U.S.  tax laws limit the time during which net
operating  loss and tax  credit  carryforwards  may be  applied  against  future
taxable income and tax  liabilities,  respectively,  Hybridon may never be fully
able to use its net  operating  loss and tax  credits  for  federal  income  tax
purposes.


Hybridon May Be Adversely Affected By Year 2000 Compliance Related Problems

        As has been widely publicized, many computer systems and microprocessors
are not  programmed  to  accommodate  dates  beyond  the year  1999.  Hybridon's
exposure  to this Y2K  problem  comes  not only from its own  internal  computer
systems and  microprocessors,  but also from the systems and  microprocessors of
its key  suppliers,  including  utility  companies and payroll  services.  While
Hybridon  believes that all of its internal systems will be Y2K compliant by the
end of the third quarter of 1999, and is taking  appropriate  measures to ensure
that its  suppliers  are Y2K  compliant,  it is  nevertheless  possible that Y2K
problems will have a material effect on Hybridon's  business.  See "Management's
Discussion And Analysis Of Financial Condition And Results Of Operations -- Year
2000."







                                       44


<PAGE>

Stock  Ownership  By  Hybridon's  Directors  And Officers May Delay Or Prevent A
Change Of Control

        Hybridon's   directors  and  executive  officers  and  their  affiliates
beneficially own a significant percentage of Hybridon's outstanding Common Stock
and Convertible  Preferred  Stock. As a result,  these  stockholders,  if acting
together,  may have the ability to influence  the outcome of  corporate  actions
requiring  stockholder  approval.  This  concentration of ownership may have the
effect of delaying or preventing a change in control of Hybridon.


ITEM 7A.       QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT
               MARKET RISK

        Historically,   Hybridon's   primary  exposures  have  been  related  to
nondollar-denominated  operating  expenses in Europe.  As of December  31, 1998,
Hybridon's assets and liabilities  related to  nondollar-denominated  currencies
were not material.


ITEM. 8.       FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA

        All  financial  statements  required to be filed  hereunder are filed as
APPENDIX A hereto,  are listed under Item 14(a), and are incorporated  herein by
this reference.


ITEM 9. CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON
        ACCOUNTING AND FINANCIAL DISCLOSURE

        None.


                                       45


<PAGE>

                                    PART III

ITEM 10.       DIRECTORS, EXECUTIVE OFFICERS AND CERTAIN SIGNIFICANT
               EMPLOYEES OF THE COMPANY

        The  response  to this  item is  contained  in part  under  the  caption
"Executive Officers and Significant  Employees of the Company" in Part I of this
Annual Report on Form 10-K and in part in the Company's  Proxy Statement for the
Annual  Meeting  of  Stockholders  to be held on June 8, 1999 (the  "1999  Proxy
Statement"),  under the  caption  "Election  of  Directors,"  which  section  is
incorporated  herein by this  reference.  The 1999 Proxy Statement will be filed
with the Securities and Exchange  Commission (the  "Commission")  not later than
120 days after the fiscal year covered by this Annual Report on Form 10-K.

        Officers are elected on an annual basis and serve at the  discretion  of
the Board of Directors.


ITEM 11.       COMPENSATION OF EXECUTIVE OFFICERS

        The response to this item is contained in the 1999 Proxy Statement under
the caption  "Election of Directors,"  which section is  incorporated  herein by
this  reference.  The 1999 Proxy Statement will be filed with the Commission not
later than 120 days after the fiscal year covered by this Annual  Report on Form
10-K.


ITEM 12.       SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND
               MANAGEMENT

        The response to this item is contained in the 1999 Proxy Statement under
the caption "Stock Ownership of Certain Beneficial Owners and Management," which
section is incorporated herein by this reference.  The 1999 Proxy Statement will
be filed with the  Commission  not later  than 120 days  after the  fiscal  year
covered by this Annual Report on Form 10-K.


ITEM 13.       CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS

        The response to this item is contained in the 1999 Proxy Statement under
the caption "Certain  Relationships and Related  Transactions," which section is
incorporated  herein by this  reference.  The 1999 Proxy Statement will be filed
with the  Commission  not later than 120 days after the fiscal  year  covered by
this Annual Report on Form 10-K.


                                       46


<PAGE>

                                     PART IV

ITEM 14.       EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS
               ON FORM 8-K

(a)   (1)   Financial Statements. Reference is made to the Index to Consolidated
            Financial  Statements  under  Item 8 of this  Annual  Report on Form
            10-K.

      (2)   The Company is not filing any financial  statement schedules as part
            of this Annual  Report on Form 10-K because they are not  applicable
            or the required  information is included in the financial statements
            or notes thereto.

      (3)   The list of Exhibits  filed as a part of this Annual  Report on Form
            10-K are set forth on the Exhibit Index  immediately  preceding such
            Exhibits, and is incorporated herein by this reference.


(b)   Reports on Form 8-K.  During the fourth  quarter of 1998,  the Company did
      not file any reports on Forms 8-K.

(c)   Exhibits  required  by Item 601 of  Regulation  S-K with  each  management
      contract,   compensatory   plan  or  arrangement   required  to  be  filed
      identified.


Exhibit No.           Description
- -----------           -----------

3.1(1)      Restated Certificate of Incorporation of the Registrant, as amended.

3.2(2)      Amended and Restated By-Laws of the Registrant.

3.3(3)      Form of Certificate of Designation of Series A Preferred Stock.

3.4(3)      Form of Certificate of Designation of Series B Preferred Stock.

4.1(2)      Specimen Certificate for shares of Common Stock, $.001 par value, of
            the Registrant.

4.2(4)      Indenture  dated as of March 26, 1997 between Forum Capital  Markets
            LLC and the Registrant.

4.3(7)      Certificate of Designation  of Series A Preferred  Stock,  par value
            $.01 per share, dated May 5, 1998.

4.4(7)      Class A Warrant Agreement dated May 5, 1998.

4.5(7)      Class B Warrant Agreement dated May 5, 1998.

4.6(7)      Class C Warrant Agreement dated May 5, 1998.

4.7(7)      Class D Warrant Agreement dated May 5, 1998.


                                       47


<PAGE>

+10.1(2)    License  Agreement  dated  February  21,  1990  and  restaged  as of
            September  8,  1993  between  the   Registrant   and  the  Worcester
            Foundation for Biomedical Research, Inc., as amended.

+10.2(2)    Patent  License  Agreement  dated  September  21,  1995  between the
            Registrant and National Institutes of Health.

+10.3(2)    Patent  License  Agreement  effective as of October 13, 1994 between
            the Registrant and McGill University.

+10.4(2)    License  Agreement  effective  as of October  25,  1995  between the
            Registrant and the General Hospital Corporation.

+10.5(2)    License   Agreement  dated  as  of  October  30,  1995  between  the
            Registrant and Yoon S. Cho-Chung.

+10.6(2)    Collaborative  Study  Agreement  effective  as of December  30, 1992
            between the Registrant and Medtronic, Inc.

+10.7(2)    System  Design and  Procurement  Agreement  dated as of December 16,
            1994 between the Registrant and Pharmacia Biotech, Inc.

10.8(2)     Lease dated March 10, 1994  between  the  Registrant  and  Laborer's
            Pension/Milford  Investment  Corporation  for space  located at 155.
            Fortune  Boulevard,  Milford,  Massachusetts,  including Note in the
            original principal amount of $750,000.

10.9(2)     Registration  Rights Agreement dated as of February 21, 1990 between
            the Registrant,  the Worcester  Foundation for Biomedical  Research,
            Inc. and Paul C. Zamecnik.

10.10(2)    Registration  Rights Agreement dated as of June 25, 1990 between the
            Registrant and Nigel L. Webb.

10.11(2)    Registration  Rights  Agreement dated as of February 6, 1992 between
            the Registrant and E. Andrews Grinstead, III.

10.12(2)    Registration  Rights  Agreement dated as of February 6, 1992 between
            the Registrant and Anthony J. Payne.

++10.13(2)  1990 Stock Option Plan, as amended.

++10.14(2)  1995 Stock Option Plan.

++10.15(2)  1995 Director Stock Plan.

++10.16(2)  1995 Employee Stock Purchase Plan.


                                       48


<PAGE>

10.17(2)    Form of Warrant  originally issued to Pillar  Investment  Limited to
            purchase  shares of Common Stock issued as placement  commissions in
            connection with the sale of shares of Series F Convertible Preferred
            Stock  and  in  consideration  of  financial  advisory  service,  as
            amended.

10.18(2)    Warrant  issued to Pillar S.A. to purchase  100,000 shares of Common
            Stock dated as of March 1, 1994, as amended.

10.19(2)    Warrant  issued to Pillar S.A. to purchase  100,000 shares of Common
            Stock dated as of March 1, 1995.

10.20(2)    Form of Warrant  issued to Pillar  Investment  Limited  to  purchase
            shares of Common Stock issued as placement commissions in connection
            with the sale of Units pursuant to the Series G Agreement.

++10.21(5)  Employment   Agreement  dated  as  of  March  1,  1997  between  the
            Registrant and E. Andrews Grinstead, III.

10.22(2)    Indemnification  Agreement  dated as of February 6, 1992 between the
            Registrant and E. Andrews Grinstead, III.

++10.23(6)  Employment  Agreement dated March 1, 1997 between the Registrant and
            Dr. Sudhir Agrawal.

++10.24(2)  Consulting  Agreement  dated as of  February  21,  1990  between the
            Registrant and Dr. Paul C. Zamecnik.

10.25(2)    Master  Lease  Agreement  dated  as of  March 1,  1994  between  the
            Registrant and General Electric Capital Corporation.

+10.26(6)   Research,  Development and License Agreement dated as of January 24,
            1996 between the Registrant and G.D. Searle & Co.

+10.27(6)   Manufacturing  and Supply  Agreement  dated as of January  24,  1996
            between the Registrant and G.D. Searle & Co.

10.28(6)    Registration  Rights  Agreement dated as of January 24, 1996 between
            the Registrant and G.D. Searle & Co.

10.29(5)    Loan and  Security  Agreement  dated as of December 31, 1996 between
            the Registrant and Silicon Valley Bank.

10.30(7)    First Amendment to Loan and Security  Agreement dated March 30, 1998
            between Hybridon, Inc. and Silicon Valley Bank.

10.31(8)    Second Amendment to Loan and Security  Agreement dated May 19, 1998,
            effective as of April 30, 1998,  between Hybridon,  Inc. and Silicon
            Valley Bank.


                                       49


<PAGE>

10.32(9)    Third  Amendment to Loan and Security  Agreement dated September 18,
            1998 between Hybridon, Inc. and Silicon Valley Bank.

10.33(9)    Fourth  Amendment to Loan and Security  Agreement  dated October 30,
            1998, effective as of September 29, 1998 between Hybridon,  Inc. and
            Silicon Valley Bank.

10.34       Fifth  Amendment to Loan and Security  Agreement  dated  December 4,
            1998 between Hybridon, Inc. and Silicon Valley Bank.

10.35(5)    Warrant issued to Silicon  Valley Bank to purchase  65,000 shares of
            Common Stock dated as of December 31, 1996.

10.36(5)    Registration  Rights Agreement dated as of December 31, 1996 between
            the Registrant and Silicon Valley Bank.

+10.37(5)   Supply and Sales Agreement dated as of September 1, 1996 between the
            Registrant and P.E. Applied Biosystems.

10.38(2)    Registration  Rights  Agreement  dated as of March 26, 1997  between
            Forum Capital Markets LLC and the Registrant.

10.39(2)    Warrant  Agreement  dated as of March 26, 1997 between Forum Capital
            Markets LLC and the Registrant.

+10.40(6)   Amendment No. 1 to License Agreement, dated as February 21, 1990 and
            restated as of  September  8, 1993,  by and  between  the  Worcester
            Foundation for Biomedical Research,  Inc. and the Registrant,  dated
            as of November 26, 1996.

10.41(10)   Letter  Agreement  dated May 12,  1997  between the  Registrant  and
            Pillar S.A.  amending the Consulting  Agreement dated as of March 1,
            1994 between the Registrant and Pillar S.A.

10.42(10)   Amendment dated July 15, 1997 to the Series G Convertible  Preferred
            Stock and Warrant  Purchase  Agreement dated as of September 9, 1994
            among the Registrant and certain purchasers, as amended.

10.43(1)    Consent Agreement dated January 15, 1998 between Silicon Valley Bank
            and the Registrant relating to the Silicon Agreement.

10.44(11)   Letter  Agreement  between the Registrant and Forum Capital  Markets
            LLC and Pecks Management  Partners Ltd. for the purchase of the Loan
            and Security Agreement with Silicon Valley Bank.

10.45(7)    Financial   Advisory   Agreement   between   Registrant  and  Pillar
            Investments Ltd. dated May 5, 1998.

10.46(7)    Placement Agency Agreement between Registrant and Pillar Investments
            Ltd. dated as of January 15, 1998.


                                       50


<PAGE>

+++10.47    Licensing  Agreement  dated March 12, 1999 by and between  Hybridon,
            Inc. and Integrated DNA Technologies, Inc.

21.1(2)     Subsidiaries of the Registrant.

23.1        Consent of Arthur Andersen LLP.

23.2        Consent of McDonnell Boehnen Hulbert & Berghoff.

27.1        Financial Data Schedule [EDGAR] - Year Ended December 31, 1998
- ------------------------------------------------

(1)         Incorporated  by  reference to Exhibits to the  Registrant's  Annual
            Report on Form 10-K for the year ended December 31, 1997.

(2)         Incorporated   by   reference   to  Exhibits  to  the   Registrant's
            Registration Statement on Form S-1 (File No. 33-99024).

(3)         Incorporated  by  reference to Exhibit  9(a)(1) to the  Registrant's
            Schedule 13E-4 dated February 6, 1998.

(4)         Incorporated  by reference to Exhibits to the  Registrant's  Current
            Report on Form 8-K dated April 2, 1997.

(5)         Incorporated  by  reference to Exhibits to the  Registrant's  Annual
            Report on Form 10-K for the year ended December 31, 1996.

(6)         Incorporated  by  reference to Exhibits to the  Registrant's  Annual
            Report on Form 10-K for the year ended December 31, 1995.

(7)         Incorporated by reference to Exhibits to the Registrant's  Quarterly
            Report on Form 10-Q for the period ended March 31, 1998.

(8)         Incorporated by reference to Exhibits to the Registrant's  Quarterly
            Report on Form 10-Q for the period ended June 30, 1998.

(9)         Incorporated by reference to Exhibits to the Registrant's  Quarterly
            Report on Form 10-Q for the period ended September 30, 1998.

(10)        Incorporated by reference to Exhibits to the Registrant's  Quarterly
            Report on Form 10-Q for the period ended June 30, 1997.

(11)        Incorporated   by   reference   to  Exhibits  to  the   Registrant's
            Registration Statement on Form S-1 (File No. 333-69649).

+           Confidential  treatment  granted  as  to  certain  portions,   which
            portions are omitted and filed separately with the Commission.


                                       51


<PAGE>

++          Management contract or compensatory plan or arrangement  required to
            be filed as an  Exhibit  to the  Annual  Report on Form 10-K for the
            year ended December 31, 1997.

+++         Confidential  treatment  requested  as to  certain  portions,  which
            portions are omitted and filed separately with the Commission.


                                       52


<PAGE>

                                   SIGNATURES

        Pursuant to the  requirements  of Section 13 or 15(d) of the  Securities
Exchange Act of 1934, as amended,  the Registrant has duly caused this report to
be signed on its behalf by the undersigned,  thereunto duly authorized,  on this
15th day of April 1999.


                                           Hybridon, Inc.

                                           /s/ E. Andrews Grinstead, III
                                           -----------------------------
                                           E. Andrews Grinstead, III
                                           Chairman of the Board, President and
                                           Chief Executive Officer


                        POWER OF ATTORNEY AND SIGNATURES

        We, the  undersigned  officers and directors of Hybridon,  Inc.,  hereby
severally  constitute  and  appoint  E.  Andrews  Grinstead,  III and  Robert G.
Andersen,  and each of them  singly,  our true and lawful  attorneys,  with full
power  to them  and  each of them  singly,  to sign  for us in our  names in the
capacities  indicated  below, all amendments to this Annual Report on Form 10-K,
and generally to do all things in our names and on our behalf in such capacities
to  enable  Hybridon,  Inc.  to comply  with the  provisions  of the  Securities
Exchange Act of 1934, as amended,  and all  requirements  of the  Securities and
Exchange Commission.

        Pursuant to the requirements of the Securities  Exchange Act of 1934, as
amended, this report has been signed below by the following persons on behalf of
the Registrant and in the capacities and on the dates indicated.


Signatures                         Titles                        Date

/s/ E. Andrews Grinstead, III      Chairman, Chief Executive     April 15, 1999
- -----------------------------      Officer and Director
E. Andrews Grinstead, III


/s/ Robert G. Andersen             Treasurer (Principal          April 15, 1999
- -----------------------------      Financial and Accounting
Robert G. Andersen                 Officer)


                                   Senior Vice President and
- -----------------------------      Director
Sudhir Agrawal, D. Phil.


/s/ James B. Wyngaarden
- -----------------------------      Director                      April 14, 1999
James B. Wyngaarden, Ph.D.


- -----------------------------      Director
Nasser Menhall


/s/ Paul C. Zamecnik               Director                      April 15, 1999
- -----------------------------
Paul C. Zamecnik, Ph.D.


/s/ Youssef El-Zein                Director                      April 15, 1999
- -----------------------------
Youssef El-Zein


<PAGE>

/s/ Arthur W. Berry                Director                      April 15, 1999
- -----------------------------
Arthur W. Berry


/s/ Harold L. Purkey               Director                      April 15, 1999
- -----------------------------
Harold L. Purkey


/s/ Camille Chebeir                Director                      April 15, 1999
- -----------------------------
Camille Chebeir


/s/ H.F. Powell                    Director                      April 15, 1999
- -----------------------------
H.F. Powell


/s/ Mohamed El-Khereij             Director                      April 15, 1999
- -----------------------------
Mohamed El-Khereij


                                       54


<PAGE>

                                   APPENDIX A





                                      INDEX

                                                                            PAGE

REPORT OF INDEPENDENT PUBLIC ACCOUNTANTS                                    F-2

CONSOLIDATED BALANCE SHEETS                                                 F-3

CONSOLIDATED STATEMENTS OF OPERATIONS                                       F-4

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT)                   F-5

CONSOLIDATED STATEMENTS OF CASH FLOWS                                       F-7

NOTES TO CONSOLIDATED FINANCIAL STATEMENTS                                  F-8





                                            F-1



<PAGE>

                    REPORT OF INDEPENDENT PUBLIC ACCOUNTANTS


To Hybridon, Inc.:

We have audited the accompanying  consolidated balance sheets of Hybridon,  Inc.
(a Delaware  corporation) and subsidiaries as of December 31, 1997 and 1998, and
the  related  consolidated   statements  of  operations,   stockholders'  equity
(deficit)  and cash  flows  for each of the  three  years  in the  period  ended
December 31, 1998.  These  financial  statements are the  responsibility  of the
Company's  management.  Our  responsibility  is to  express  an opinion on these
financial statements based on our audits.

We  conducted  our  audits  in  accordance  with  generally   accepted  auditing
standards.  Those standards require that we plan and perform the audit to obtain
reasonable assurance about whether the financial statements are free of material
misstatement.  An audit includes examining, on a test basis, evidence supporting
the amounts and disclosures in the financial statements.  An audit also includes
assessing the  accounting  principles  used and  significant  estimates  made by
management,  as well as evaluating the overall financial statement presentation.
We believe that our audits provide a reasonable basis for our opinion.

In our opinion,  the financial  statements  referred to above present fairly, in
all material respects, the financial position of Hybridon, Inc. and subsidiaries
as of  December  31,  1997  and  1998  and the  consolidated  results  of  their
operations  and their cash flows for each of the three years in the period ended
December 31, 1998, in conformity with generally accepted accounting principles.

The accompanying  consolidated  financial statements have been prepared assuming
that the Company will continue as a going concern. Since inception,  the Company
has incurred significant losses which it has funded through the issuance of debt
and equity  securities and through research and development  collaborations  and
licensing  agreements.  The Company  expects such  resources to fund  operations
through May 1999.  There is  substantial  doubt about the  Company's  ability to
continue as a going concern.  See Note 1 for  management's  plans. The financial
statements do not include any adjustments  that might result from the outcome of
this uncertainty.



                                                         /s/ ARTHUR ANDERSEN LLP



Boston, Massachusetts
February 19, 1999  (except with 
respect to the matter disclosed 
in Note 7(b) as to which the date 
is April 15, 1999)



                                       F-2



<PAGE>

                                          HYBRIDON, INC. AND SUBSIDIARIES

                                            CONSOLIDATED BALANCE SHEETS

                                                        ASSETS
<TABLE>
<CAPTION>

                                                                                                December 31,
                                                                                           1997              1998
<S>                                                                                  <C>              <C>    

CURRENT ASSETS:
     Cash and cash equivalents                                                        $     2,202,202  $     5,607,882
     Accounts receivable                                                                      529,702        1,175,441
     Prepaid expenses and other current assets                                              1,005,825          110,827
                                                                                      ---------------  ---------------

         Total current assets                                                               3,737,729        6,894,150
                                                                                      ---------------  ---------------

PROPERTY AND EQUIPMENT, AT COST:
     Leasehold improvements                                                                16,027,734       11,127,035
     Laboratory and other equipment                                                        14,288,083       11,432,435
                                                                                      ---------------  ---------------
                                                                                           30,315,817       22,559,470

     Less-Accumulated depreciation and amortization                                        11,085,013       13,788,979
                                                                                      ---------------  ---------------

                                                                                           19,230,804        8,770,491
                                                                                      ---------------  ---------------
OTHER ASSETS:
     Deferred financing costs and other assets                                              3,354,767          612,374
     Note receivable from officer                                                             247,250          258,650
     Restricted cash                                                                        3,050,982                -
     Investment in real estate partnership                                                  5,450,000                -
                                                                                      ---------------  ---------------
                                                                                           12,102,999          871,024
                                                                                      ---------------  ---------------

                                                                                      $    35,071,532  $    16,535,665
                                                                                      ===============  ===============

                                    LIABILITIES AND STOCKHOLDERS' EQUITY (DEFICIT)
CURRENT LIABILITIES:
         Current portion of long-term debt                                            $     7,868,474  $     6,070,951
         Accounts payable                                                                   8,051,817        2,368,163
         Accrued expenses                                                                  11,917,298        4,068,679
                                                                                      ---------------  ---------------

                  Total current liabilities                                                27,837,589       12,507,793
                                                                                      ---------------  ---------------

LONG-TERM DEBT, NET OF CURRENT PORTION                                                      3,282,123          473,094
                                                                                      ---------------  ---------------

9% CONVERTIBLE SUBORDINATED NOTES PAYABLE                                                  50,000,000        1,306,000
                                                                                      ---------------  ---------------

COMMITMENTS AND CONTINGENCIES (Notes 11 and 16)

STOCKHOLDERS' EQUITY (DEFICIT):
     Preferred stock, $.01 par value-
                           Authorized-5,000,000 shares
                  Series A convertible preferred stock-
             Designated-1,500,000 shares
             Issued and outstanding-641,259 shares at December 31, 1998                             -            6,413
                  (Liquidation preference of $65,168,048 at December 31, 1998)
     Common stock, $.001 par value-
         Authorized-100,000,000 shares
         Issued and outstandingC5,059,650 and 15,304,825 shares at December 31,
         1997 and 1998, respectively                                                            5,060           15,305
     Additional paid-in capital                                                           173,695,698      241,632,024
     Accumulated deficit                                                                 (218,655,101)    (238,447,837)
     Deferred compensation                                                                 (1,093,837)        (957,127)
                                                                                      ---------------  ---------------
         Total stockholders' (deficit) equity                                             (46,048,180)       2,248,778
                                                                                      ---------------  ---------------
                                                                                      $    35,071,532  $    16,535,665
                                                                                      ===============  ===============

</TABLE>

              The accompanying  notes are an integral part of these consolidated
financial statements.





                                      F-3

<PAGE>

                                          HYBRIDON, INC. AND SUBSIDIARIES

                                       CONSOLIDATED STATEMENTS OF OPERATIONS

<TABLE>
<CAPTION>

                                                                                  Years Ended December 31,
                                                                          1996              1997             1998
<S>                                                               <C>                 <C>              <C>   

REVENUES:
     Product and service                                            $   1,080,175     $   1,876,862    $   3,253,879
     Research and development                                           1,419,389           945,000        1,099,915
     Royalty and other income                                              62,321            48,000                -
     Interest                                                           1,446,762         1,079,122          148,067
                                                                    -------------     -------------    -------------

                                                                        4,008,647         3,948,984        4,501,861
                                                                    -------------     -------------    -------------

OPERATING EXPENSES:
     Research and development                                          39,390,525        46,827,915       20,977,370
     General and administrative                                        11,346,670        11,026,748        6,572,502
     Interest                                                             124,052         4,535,647        2,932,362
     Restructuring                                                              -        11,020,000                -
                                                                    -------------     -------------    -------------
                  Total operating expenses                             50,861,247        73,410,310       30,482,234
                                                                    -------------     -------------    -------------

                  Loss before extraordinary item                      (46,852,600)      (69,461,326)     (25,980,373)

EXTRAORDINARY ITEM:
     Gain on exchange of 9% convertible subordinated                            -                 -        8,876,685
     notes payable                                                  -------------     -------------    -------------

                  Net Loss                                            (46,852,600)      (69,461,326)     (17,103,688)

ACCRETION OF PREFERRED STOCK DIVIDENDS                                          -                 -        2,689,048
                                                                    -------------     -------------    -------------

                  Net loss applicable to common stockholders        $ (46,852,600)    $ (69,461,326)   $ (19,792,736)
                                                                    =============     =============    =============

BASIC AND DILUTED NET LOSS PER COMMON SHARE:

                  Loss per share before extraordinary item          $      (10.24)    $      (13.76)   $       (2.19)

                  Extraordinary item                                                                            0.75
                                                                                -                 -
                                                                    -------------     -------------    -------------

                  Net loss per share                                       (10.24)           (13.76)           (1.44)

                  Accretion of preferred stock dividends                        -                 -             (.23)
                                                                    -------------     -------------    -------------




                 Net loss per share applicable to common            
                 stockholders                                       $      (10.24)    $      (13.76)   $       (1.67)
                                                                    =============     =============    =============
             

SHARES USED IN COMPUTING BASIC                                          
AND DILUTED NET LOSS PER COMMON SHARE                                   4,575,555         5,049,840       11,859,350
                                                                    =============     =============    =============

</TABLE>



              The accompanying  notes are an integral part of these consolidated
financial statements.


                                            F-4



<PAGE>

                                     HYBRIDON, INC. AND SUBSIDIARIES

                       CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT)



<TABLE>
<CAPTION>

                                                         Convertible          Series A Convertible           Common Stock
                                                       Preferred Stock           Preferred Stock
                                                   Number of     $.01 Par    Number of     $.01 Par     Number of    $.001 Par   
                                                     Shares       Value        Shares       Value        Shares        Value     
                                                                                                                                 
<S>                                                <C>           <C>         <C>            <C>          <C>          <C>

BALANCE, DECEMBER 31, 1995                           3,196,435   $   31,965            -  $         -       368,733   $      369 

Issuance of common stock related to initial 
   public offering, net of issuance costs of
   $5,268,756                                                -            -            -            -     1,150,000        1,150 
Conversion of convertible preferred stock
   to common stock                                  (3,196,435)     (31,965)           -            -     3,371,330        3,371 
Issuance of common stock related to the
   exercise of stock options                                 -            -            -            -        57,740           58 
Issuance of common stock related to the
   exercise of warrants                                      -            -            -            -        81,512           81 
Deferred compensation related to grants
   of stock options to nonemployees                          -            -            -            -             -            - 
Amortization of deferred compensation                        -            -            -            -             -            - 
    Net loss                                                 -            -            -            -             -            - 
                                                   -----------   ----------  -----------   ----------   -----------   ---------- 

BALANCE, DECEMBER 31, 1996                                   -            -            -            -     5,029,315        5,029 
Issuance of common stock related to the
    exercise of stock                                        -            -            -            -        25,005           26 
Issuance of common stock related to the
    exercise of warrants                                     -            -            -            -           330            - 
Issuance of common stock for services
    rendered                                                 -            -            -            -         5,000            5   
Deferred compensation related to grants
    of stock options to nonemployees                         -            -            -            -             -            -   
Amortization of deferred compensation                        -            -            -            -             -            -   
    Net loss                                                 -            -            -            -             -            -   
                                                   -----------   ----------  -----------   ----------   -----------   ----------  

BALANCE, DECEMBER 31, 1997                                   -            -            -            -     5,059,650        5,060  


                                                     Additional   Accumulated       Deferred         Total
                                                      Paid-in       Deficit       Compensation    Stockholders'
                                                      Capital                                    Equity (Deficit)

BALANCE, DECEMBER 31, 1995                          $114,755,394  $(102,341,175)  $        -      $ 12,446,553

Issuance of common stock related to initial 
   public offering, net of issuance costs of
   $5,268,756                                         52,230,094              -            -        52,231,244
Conversion of convertible preferred stock
   to common stock                                        28,594              -            -                 -
Issuance of common stock related to the
   exercise of stock options                           1,089,618              -            -         1,089,676
Issuance of common stock related to the
   exercise of warrants                                3,176,660              -            -         3,176,741
Deferred compensation related to grants
   of stock options to nonemployees                    1,967,116              -   (1,967,116)                -
Amortization of deferred compensation                          -              -      763,190           763,190
    Net loss                                                   -    (46,852,600)           -       (46,852,600)
                                                    ------------  -------------  -----------      ------------
BALANCE, DECEMBER 31, 1996                           173,247,476   (149,193,775)  (1,203,926)       22,854,804
Issuance of common stock related to the
    exercise of stock                                     86,300              -            -            86,326
Issuance of common stock related to the
    exercise of warrants                                   9,075              -            -             9,075
Issuance of common stock for services
    rendered                                             146,869              -            -           146,874
Deferred compensation related to grants
    of stock options to nonemployees                     205,978              -     (205,978)                -
Amortization of deferred compensation                          -              -      316,067           316,067
    Net loss                                                   -    (69,461,326)           -       (69,461,326)
                                                    ------------  -------------  -----------      ------------
BALANCE, DECEMBER 31, 1997                           173,695,698   (218,655,101)  (1,093,837)      (46,048,180)

</TABLE>

                                            F-5



<PAGE>

                                      HYBRIDON, INC. AND SUBSIDIARIES

                      CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT)
                                              (Continued)

<TABLE>
<CAPTION>

                                                              Convertible          Series A Convertible           Common Stock
                                                            Preferred Stock           Preferred Stock
                                                        Number of     $.01 Par    Number of     $.01 Par     Number of    $.001 Par
                                                          Shares       Value        Shares       Value        Shares        Value 


<S>                                                         <C>           <C>   <C>             <C>       <C>             <C>
   Issuance of Series A convertible preferred stock
     and attached warrants in exchange for
     conversion of 9% convertible                            --           --      510,504        5,105         --           -- 
     subordinated notes payable and accrued interest                  
   Issuance of common stock and attached                              
     warrants in exchange for conversion of                  --           --         --           --      3,217,154        3,217
     accounts payable and other obligations                           
   Issuance of Series A convertible preferred stock          --           --      114,285        1,143         --           -- 
Issuance of Common Stock to Placement Agent                  --           --         --           --        597,699          598
   Issuance of common stock and attached                              
     warrants in  exchange for conversion                    --           --         --           --      3,157,322        3,157
     of convertible notes payable, net of                             
     issuance costs of $566,167                                       
   Issuance of common stock and attached                              
     warrants, net of issuance  costs of                     --           --         --           --      3,223,000        3,223
     $1,069,970                                                                                                                 
   Issuance of common stock for services                     --           --         --           --         50,000           50
     rendered                                                         
   Deferred compensation related to grants                            
     of stock options to nonemployees,                       --           --         --           --           --           -- 
     net of terminations                                              
   Issuance of warrants in connection with                   --           --         --           --           --           -- 
     notes payable                                                    
   Accretion and issuance of Series A                                 
     convertible preferred                                   --           --       16,470          165         --           -- 
         stock dividends                                              
   Amortization of deferred compensation                     --           --         --           --           --           -- 
   Net loss                                                  --           --         --           --           --           -- 
                                                        -------     --------   ----------   ----------   ----------   ----------
BALANCE, DECEMBER 31, 1998                                   --     $     --      641,259   $    6,413   15,304,825   $   15,305
                                                        =======     ========   ==========   ==========   ==========   ==========
</TABLE>


<TABLE>
<CAPTION>

                                                                    Additional        Accumulated      Deferred          Total
                                                                 Paid-in Capital         Deficit      Compensation    Stockholders'
                                                                                                                          Equity 
                                                                                                                        (Deficit)

<S>                                                               <C>                     <C>               <C>         <C>
   Issuance of Series A convertible preferred stock
     and attached warrants in exchange for
     conversion of 9% convertible                                   39,924,887             --                --          39,929,992
     subordinated notes payable and accrued interest
   Issuance of common stock and attached
     warrants in exchange for conversion of                          5,931,341             --                --           5,934,558
     accounts payable and other obligations
   Issuance of Series A convertible preferred stock                  7,998,817             --                --           7,999,960
Issuance of Common Stock to Placement Agent                          1,194,800             --                --           1,195,398
   Issuance of common stock and attached
     warrants in  exchange for conversion                            4,230,676             --                --           4,233,833
     of convertible notes payable, net of
     issuance costs of $566,167
   Issuance of common stock and attached
     warrants, net of issuance  costs of                             6,873,453             --                --           6,876,676
     $1,069,970                                                                                                                     
   Issuance of common stock for services                                93,700             --                --              93,750
     rendered
   Deferred compensation related to grants
     of stock options to nonemployees,                                 109,734             --            (109,734)             --
     net of terminations
   Issuance of warrants in connection with                              85,433             --                --              85,433
     notes payable
   Accretion and issuance of Series A
     convertible preferred                                           2,688,883       (2,689,048)             --                --
         stock dividends
   Amortization of deferred compensation                                  --               --             246,444           246,444
   Net loss                                                               --        (17,103,688)             --         (17,103,688)
                                                                 -------------    -------------     -------------     -------------
BALANCE, DECEMBER 31, 1998                                       $ 241,632,024    $(238,447,837)    $    (957,127)    $   2,248,778
                                                                 =============    =============     =============     =============
</TABLE>

              The accompanying  notes are an integral part of these consolidated
financial statements.



                                      F-6

<PAGE>

<TABLE>
<CAPTION>
                                          HYBRIDON, INC. AND SUBSIDIARIES

                                       CONSOLIDATED STATEMENTS OF CASH FLOWS

                                                                                            Years Ended December 31,
                                                                                    1996                1997               1998
CASH FLOWS FROM OPERATING ACTIVITIES:
<S>                                                                              <C>                <C>                <C>          
    Net loss                                                                     $(46,852,600)      $(69,461,326)      $(17,103,688)
    Adjustments to reconcile net loss to net cash used in
  operating activitiesB
       Extraordinary gain on exchange of 9% convertible                                  --                 --           (8,876,685)
  subordinated notes payable
       Depreciation and amortization                                                2,393,751          4,488,719          4,057,286
       Issuance of common stock for services rendered                                    --              146,874             93,750
       Amortization of deferred compensation                                          763,190            316,067            246,444
       Amortization of deferred financing costs                                          --              479,737            160,813
       Noncash portion of restructuring charge                                           --            1,255,000               --
       Changes in assets and liabilitiesB
          Accounts receivable                                                        (573,896)            44,194           (645,739)
          Prepaid expenses and other current assets                                  (593,797)           539,499            894,998
          Note receivable from officer                                                 (9,845)            70,728            (11,400)
          Accounts payable                                                          2,010,981          3,987,398         (3,059,002)
          Accrued expenses                                                            736,141          7,071,532          1,565,806
          Deferred revenue                                                               --              (86,250)              --
          Amounts payable to related parties                                          (12,500)              --
                                                                                 ------------       ------------       ------------
             Net cash used in operating activities                                (42,138,575)       (51,147,828)       (22,677,417)
                                                                                 ------------       ------------       ------------
CASH FLOWS FROM INVESTING ACTIVITIES:
    (Increase) decrease in short-term investments                                  (3,785,146)         3,785,146               --
    Purchases of property and equipment                                            (8,902,989)        (7,509,755)          (471,949)
    Proceeds from sale of property and equipment                                         --                 --              714,400
    (Investment in) sale of real estate partnership                                (3,751,552)         5,450,000
                                                                                 ------------       ------------       ------------
             Net cash (used in) provided by investing activities                  (16,439,687)        (3,724,609)         5,692,451
                                                                                 ------------       ------------       ------------
CASH FLOWS FROM FINANCING ACTIVITIES:
    Proceeds from issuance of Series A convertible preferred stock                       --                 --            7,999,960
    Proceeds from issuance of common stock related to stock                         1,089,676             86,326               --
    options and restricted stock grants
    Net proceeds from issuance of common stock                                     52,231,244               --            6,876,676
    Proceeds from notes payable                                                     7,500,000               --            6,000,000
    Proceeds from issuance of convertible promissory notes payable                       --           50,000,000          4,233,833
    Proceeds from issuance of common stock related to stock                         3,176,741              9,075               --
    warrants
    Proceeds from sale/leaseback of fixed assets                                    1,722,333          1,205,502               --
    Payments on long-term debt                                                       (446,163)        (1,564,268)        (7,296,646)
    Decrease (increase) in deferred financing costs                                   251,921         (2,820,790)          (400,000)
    Decrease (increase) in restricted cash and other assets                           401,990         (2,474,948)         2,976,823
                                                                                 ------------       ------------       ------------
             Net cash provided by financing activities                             65,927,742         44,440,897         20,390,646
                                                                                 ------------       ------------       ------------
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS                                7,349,480        (10,431,540)         3,405,680
CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR                                        5,284,262         12,633,742          2,202,202
                                                                                 ------------       ------------       ------------
CASH AND CASH EQUIVALENTS, END OF YEAR                                           $ 12,633,742       $  2,202,202       $  5,607,882
                                                                                 ============       ============       ============
</TABLE>



   The accompanying notes are an integral part of these  consolidated  financial
statements.



                                                   F-7



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998





(1)   ORGANIZATION

      Hybridon,  Inc. (the Company) was incorporated in the State of Delaware on
      May 25, 1989.  The Company is engaged in the discovery and  development of
      novel genetic medicines based primarily on antisense technology.

      Since inception,  the Company has devoted substantially all of its efforts
      toward product research and development, its custom contract manufacturing
      business  (Hybridon  Specialty  Products  or  HSP)  and  raising  capital.
      Management  anticipates  that  substantially  all future  revenues will be
      derived  from the sale of  proprietary  biopharmaceutical  products  under
      development  or to  be  developed  in  the  future,  and  custom  contract
      manufacturing  of synthetic DNA products and reagent products (by HSP), as
      well as from  research and  development  revenues  and fees and  royalties
      derived from licensing of the Company's technology.  Accordingly, although
      the  Company  has begun to  generate  revenues  from its  custom  contract
      manufacturing  business,  the Company is dependent  on the  proceeds  from
      possible  future  sales of debt and equity  securities  and  research  and
      development  collaborations in order to fund future  operations.  There is
      substantial  doubt  concerning its ability to continue as a going concern.
      As of December  31,  1998,  the Company had cash and cash  equivalents  of
      approximately  $5.6 million.  The Company  expects such  resources to fund
      operations through May 1999. The consolidated  financial statements do not
      include  any  adjustments  that  might  result  from the  outcome  of this
      uncertainty.

      The  Comapny is curently  seeking  debt or equity  financing  in an amount
      sufficient  to support  its  operations  through  the end of 1999,  and in
      connection  therewith,  is in negotiations  with several parties to obtain
      such financing.  If the Company is unable to obtain this sufficient amount
      of  additional  funding in May 1999,  it will be forced to  terminate  its
      operations or seek relief under  applicable  bankruptcy  law by the end of
      May 1999.


      On  December  3, 1997,  the Company  was  delisted  from the Nasdaq  Stock
      Market,  Inc.  (NASDAQ) because the Company was not in compliance with the
      continued listing  requirements of the NASDAQ National Market. The Company
      is currently trading on the NASD OTC as a result of the delisting.

(2)   SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

      (a)  Management Estimates and Uncertainties

           The preparation of financial  statements in conformity with generally
           accepted accounting  principles requires management to make estimates
           and  assumptions  that  affect  the  reported  amounts  of assets and
           liabilities  and disclosure of contingent  assets and  liabilities at
           the date of the  financial  statements  and the  reported  amounts of
           revenues and expenses  during the reporting  period.  Actual  results
           could differ from those estimates.

           The Company is subject to a number of risks and uncertainties similar
           to those of other companies of the same size within the biotechnology
           industry,  such as uncertainty with clinical  trials,  uncertainty of
           additional funding and history of operating losses.



                                       F-8



<PAGE>

                                HYBRIDON, INC. AND SUBSIDIARIES



                          NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                       DECEMBER 31, 1998



                                          (Continued)



      (b)  Principles of Consolidation

           The  accompanying   consolidated  financial  statements  include  the
           results of the Company and its subsidiaries,  Hybridon S.A. (Europe),
           a  French  corporation,   and  Hybridon  Canada,  Inc.  (an  inactive
           majority-owned  subsidiary).  The consolidated  financial  statements
           also  reflect  the  Company's  30%  interest  in   MethylGene,   Inc.
           (MethylGene), a Canadian corporation which is accounted for under the
           equity method (see Note 14). All material  intercompany  balances and
           transactions have been eliminated in consolidation.

      (c)  Cash Equivalents

           The Company  considers all highly liquid  investments with maturities
           of three months or less when purchased to be cash  equivalents.  Cash
           and cash  equivalents  and  restricted  cash at December 31, 1997 and
           1998   consisted  of  the  following  (at   amortized   cost,   which
           approximates fair market value):

<TABLE>
<CAPTION>

                                                                             1997             1998
<S>                                                                      <C>               <C>

                Cash and cash equivalents-
                              Cash and money market funds                 $1,702,272       $3,865,365
                              Corporate bond                                 499,930        1,742,517
                                                                          ----------       ----------
                              Total cash and cash equivalents             $2,202,202       $5,607,882
                                                                          ==========       ==========

                Restricted cash-
                              Note payable to bank (Note 7(a))            $1,758,542       $        -
                              Foreign bank account (Note 6)                1,034,618                -
                              Capital lease obligations (Note 7(d))          257,822                -
                                                                          ----------       ----------
                                                                          $3,050,982       $        -
                                                                          ==========       ==========

</TABLE>

      (d)  Depreciation and Amortization

           Depreciation and  amortization  are computed using the  straight-line
           method based on the estimated  useful lives of the related  assets as
           follows:

                   Asset Classification           Estimated
                                                 Useful Life

             Leasehold improvements             Life of lease
             Laboratory equipment and other       3-5 years




                                       F-9



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



      (e)  Accrued Expenses

           At  December  31,  1997 and 1998,  accrued  expenses  consist  of the
following:

<TABLE>
<CAPTION>

                                                                          1997             1998
<S>             <C>                                                   <C>             <C>    

                Restructuring (Note 3)                                $8,316,148         $469,485
                Interest                                               1,125,000           29,385
                Payroll and related costs                                742,452        1,151,742
                Outside research and clinical costs                    1,231,818          797,593
                Professional fees                                        150,000          149,957
                Contingent stock (Notes 7(b) and 15(c))                        -        1,000,000
                Other                                                    351,880          470,517
                                                                     -----------       ----------
                                                                     $11,917,298       $4,068,679
                                                                     ===========       ==========
</TABLE>


      (f)  Reclassifications

           Certain   amounts  in  the  prior  periods   consolidated   financial
           statements  have  been  reclassified  to  conform  with  the  current
           period's presentation.

      (g)  Revenue Recognition

           The Company has recorded  revenue under the  consulting  and research
           agreements  discussed in Notes 8, 9 and 14.  Revenue is recognized as
           earned on a straight-line basis over the term of the agreement, which
           approximates when work is performed and costs are incurred.  Revenues
           from product and service sales are  recognized  when the products are
           shipped or the services are  performed.  Product  revenue during 1997
           and  1998  represents  revenues  from  the  sale of  oligonucleotides
           manufactured on a custom contract basis by HSP.

      (h)  Research and Development Expenses

           The Company charges  research and development  expenses to operations
           as incurred.

      (i)  Patent Costs

           The Company charges patent expenses to operations as incurred.



                                      F-10



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



      (j)  Comprehensive Loss

           The Company  applies SFAS No. 130,  Reporting  Comprehensive  Income.
           Comprehensive  loss is  defined as the change in equity of a business
           enterprise  during a period from  transactions  and other  events and
           circumstances from nonowner sources. The Company's comprehensive loss
           is the same as the reported net loss for all periods presented.

      (k)  Net Loss per Common Share

           The Company applies SFAS No 128,  Earnings per Share.  Under SFAS No.
           128,  basic net loss per common share is computed  using the weighted
           average  number  of shares of common  stock  outstanding  during  the
           period.  Diluted  net loss per common  share is the same as basic net
           loss per  common  share as the  effects  of the  Company's  potential
           common stock  equivalents are antidilutive.  Antidilutive  securities
           which consist of stock options,  warrants and  convertible  preferred
           stock (on an as-converted basis) that are not included in diluted net
           loss per common share were  2,595,496,  2,404,561 and  27,774,883 for
           1996, 1997, and 1998, respectively.

      (l)  Segment Reporting

           The Company  applies SFAS No. 131,  Disclosures  About Segments of an
           Enterprise  and  Related   Information.   SFAS  No.  131  establishes
           standards for reporting  information  regarding operating segments in
           annual  financial  statements and requires  selected  information for
           those segments to be presented in interim financial reports issued to
           stockholders.  SFAS No. 131 also  establishes  standards  for related
           disclosures  about  products and services and  geographic  areas.  To
           date,  the Company has viewed its operations and manages its business
           as  principally  one operating  segment.  As a result,  the financial
           information   disclosed  herein,   represents  all  of  the  material
           financial  information  related to the Company's  principal operating
           segment.  All of the  Company's  revenues are generated in the United
           States and substantially all assets are located in the United States.

(3)   RESTRUCTURING

      Beginning in July 1997, the Company  implemented a  restructuring  plan to
      reduce  expenditures  on a phased  basis in an effort to conserve its cash
      resources.  As part of this restructuring plan, in addition to terminating
      the  clinical  development  of GEM  91,  the  Company's  first  generation
      antisense  drug for the treatment of AIDS and HIV  infection,  the Company
      reduced or suspended  programs  unrelated to its core  advanced  chemistry
      antisense drug research and development  programs.  In connection with the
      reduction in programs, the Company has accrued termination fees related to
      research  contracts  and has written off assets  related to programs  that
      have been suspended or canceled. As part of the restructuring, all outside
      testing,  public  relations,   travel  and  entertainment  and  consulting
      arrangements   were  reviewed  and  where   appropriate   the  terms  were
      renegotiated, contracts cancelled or the terms were significantly reduced.
      As a result of the implementation of these changes, the Company terminated
      the employment of 84 employees at its



                                      F-11



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



      Cambridge  and Milford,  Massachusetts,  facilities in 1997 and closed its
      operations in Paris, France, and terminated 11 employees at that location.

      In connection with the  restructuring,  the Company entered into different
      subleasing  arrangements.  During 1997, the Company subleased a portion of
      each  of  its   facilities  in  Cambridge,   Massachusetts   (including  a
      substantial  portion of its former  headquarters  located at 620  Memorial
      Drive  (the  Cambridge  Headquarters).    The  Company  incurred  expenses
      relating  to these  subleases  for  broker  fees and  renovation  expenses
      incurred in preparing the Cambridge Headquarters space for the new tenant.
      In addition,  the Company  accrued the estimated  lease loss of subleasing
      the Cambridge  Headquarters  which were vacated  during 1998.  The Company
      also  subleased  its office in Paris,  France,  and accrued the  estimated
      lease loss.

      The following are the significant components of the $11,020,000 charge for
      restructuring (in thousands):

<TABLE>
<CAPTION>
                                                                                                    To be Paid
                                                                                                      as of
                                            Restructuring       Non-Cash         Cash              December 31,
                                               Charge           Portion        Disbursed               1998
                                               ------           -------        ---------               ----
                                            
<S>                                           <C>               <C>               <C>               <C>    
Estimated loss on facility leases             $ 6,372           $ 5,976           $   356           $    40
Employee severance, benefits and                2,738                --             2,548               190
  related costs
Write-down of assets to net realizable            946               946                --                --
 value
Termination costs of certain                      964               672                53               239
  research programs                           -------           -------           -------           -------

                                              $11,020           $ 7,594           $ 2,957           $   469
                                              =======           =======           =======           =======
</TABLE>


      The  Company   disbursed  cash  totaling   approximately   $1,453,000  and
      $1,504,000   in  1997  and  1998,   respectively,   with  respect  to  the
      restructuring. The remaining accrued amount of approximately $469,000 will
      be paid during 1999.

(4)   INVESTMENT IN REAL ESTATE PARTNERSHIP

      Under the terms of the lease for the Cambridge Headquarters (the Cambridge
      Lease), the Company accounted for $5,450,000 of its payments for a portion
      of the costs of construction of the leased  premises as  contributions  to
      the  capital  of  the  Cambridge   landlord  in  exchange  for  a  limited
      partnership interest in the Cambridge landlord (the Partnership Interest).
      Under the terms of the  Partnership  Interest,  the Company  exercised its
      right to sell back the  Partnership  Interest and received  payment of the
      $5,450,000 in 1998.



                                      F-12



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



(5)   NOTE RECEIVABLE FROM OFFICER

      At  December  31, 1997 and 1998 the  Company  has a note  receivable  from
      officer,   including   accrued   interest,   of  $247,250  and   $258,650,
      respectively.  The note has an interest rate of 6.0% per annum and matures
      in April 2001.

(6)   RESTRICTED CASH - BVH

      In November  1997,  the Company was notified by Bank Fur  Vermogensanlagen
      Und Handel AG (BVH) that the Federal Banking Supervisory Office in Germany
      had  imposed  a  moratorium  on BVH  and  had  closed  BVH  for  business.
      Accordingly,  the Company  classified  its deposit with BVH as  restricted
      cash. The Company sold the deposit to the Cambridge Landlord, an affiliate
      of certain  directors of the  Company,  and  recovered  the full amount in
      1998.

(7)   LONG-TERM DEBT AND CAPITAL LEASE OBLIGATIONS

      Future  minimum  principal  payments  due  under  various  notes  payable,
      excluding the 9% convertible  subordinated  notes (the 9% Notes) due April
      1, 2004, are as follows at December 31, 1998:

          December 31,                                        Amount
          ------------                                        ------

          1999                                            $     6,070,951
          2000                                                     80,746
          2001                                                     91,892
          2002                                                    104,576
          2003                                                    119,010
          Thereafter                                               76,870
                                                          ---------------

                 Total long-term debt obligations               6,544,045

          Less--Current portion                                 6,070,951
                                                          ---------------
                                                          $       473,094
                                                          ===============

      (a)  Note Payable to a Bank

      In December 1996,  the Company  entered into a five-year  $7,500,000  note
      payable  to  a  bank.  In  November  1998,  the  outstanding   balance  of
      approximately  $2,895,000  was  purchased  from the bank by Forum  Capital
      Markets,   LLC  (Forum)  and  certain  investors   associated  with  Pecks
      Management Partners Ltd. (Pecks)  (collectively,  the Lenders),  which are
      affiliates of two members of the Company's Board of Directors.




                                      F-13



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



      (b)  Note Payable to Lenders

      In connection  with the purchase by the Lenders of the note payable to the
      bank,  the Lenders  lent an  additional  $3,200,000  so as to increase the
      outstanding  principal amount of the note to $6,000,000.  The terms of the
      note  payable  were  amended as follows:  (i) the maturity was extended to
      November  30,  2003;  (ii) the  interest  rate was  decreased to 8%; (iii)
      interest is payable monthly in arrears,  with the principal due in full at
      maturity  of the  loan;  (iv)  the note  payable  is  convertible,  at the
      Lenders'  option,  in whole or in part,  into shares of common  stock at a
      conversion price equal to $2.40 per share; (v) the note includes a minimum
      liquidity,  as defined  covenant of $2,000,000;  and (vi) the note payable
      may not be prepaid,  in whole or in part, at any time prior to December 1,
      2000. On March 30, 1999, the Company  received a waiver for  noncompliance
      with the minimum tangible net worth covenant  effective as of December 31,
      1998 and March 31, 1999.  On April 15, 1999,  the Company also  received a
      waiver for noncompliance  with the minimun liquidity covenant effective as
      of April 15, 1999. The Company has classified the  outstanding  balance of
      $6,000,000 at December 31, 1998 as a current liability in the accompanying
      consolidated  balance sheet as it does not currently have the financing to
      remain in compliance with the financial covenants.  In connection with the
      purchase of the note payable,  Forum is entitled to receive  $400,000 as a
      fee,  which  Forum has agreed to reinvest by  purchasing  common  stock or
      preferred stock, both with attached warrants. The Company has recorded the
      $400,000 as a deferred financing cost, which will be amortized to interest
      expense over the term of the note and an accrued  expense for the issuance
      of common stock or preferred  stock,  both with attached  warrants,  which
      will occur in 1999. In addition,  Forum is entitled to receive warrants to
      purchase  $400,000  of shares of common  stock of the  Company  at the per
      share valuation of the next financing, or $3.00 per share if the financing
      is not completed by May 1, 1999.  The Company  determined the value of the
      warrants to be $85,433,  by using the Black-Scholes  option pricing model.
      The Company has recorded this $85,433 as a deferred  financing cost, which
      will be amortized to interest expense over the term of the note.

      (c)  Note Payable to Landlord

      In December  1994, the Company  issued a $750,000  promissory  note to its
      landlord  to  fund  specific   construction   costs  associated  with  the
      development  of its  manufacturing  plant in Milford,  Massachusetts.  The
      promissory note bears interest at 13% per annum and is to be paid in equal
      monthly  installments  of principal and interest over the remainder of the
      10-year lease term.

      (d)  Capital Lease Obligations

      The Company had entered into various capital leases for equipment.  During
      1998,  the Company  settled its capital lease  obligations in full through
      the issuance of common stock and warrants (see Note 15 (c)).

      (e)  9% Convertible Subordinated Notes Payable

      On April 2, 1997,  the Company issued  $50,000,000 of the 9% Notes.  Under
      the terms of the 9% Notes,  the  Company  must  make  semiannual  interest
      payments on the outstanding principal balance through the maturity date of
      April 1, 2004. If the 9% Notes are converted prior to April 1, 2000,



                                      F-14



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



      the noteholders are entitled to receive accrued  interest from the date of
      the most recent interest payment through the conversion date. The 9% Notes
      are  convertible  at any time prior to the  maturity  date at a conversion
      price   equal  to   $35.0625,   subject  to   adjustment   under   certain
      circumstances, as defined.

      Beginning April 1, 2000, the Company may redeem the 9% Notes at its option
      for a 4.5% premium over the original  issuance  price  provided  that from
      April 1, 2000 to March 31, 2001,  the 9% Notes may not be redeemed  unless
      the  closing  price of the  common  stock  equals or  exceeds  150% of the
      conversion price for a period of at least 20 out of 30 consecutive trading
      days and the 9% Notes are  redeemed  within  60 days  after  such  trading
      period.  The premium  decreases by 1.5% each year through  March 31, 2003.
      Upon a change of control of the Company,  as defined,  the Company will be
      required  to offer  to  repurchase  the 9%  Notes at 150% of the  original
      issuance price.

      On  February  6, 1998,  the Company  commenced  an  exchange  offer to the
      holders of the 9% Notes to exchange the 9% Notes for Series A  convertible
      preferred  stock  and  warrants.  On  May  5,  1998,  noteholders  holding
      $48,694,000 of principal and $2,361,850 of accrued interest  tendered such
      principal and accrued interest to the Company for 510,505 shares of Series
      A convertible preferred stock and warrants to purchase 3,002,958 shares of
      common stock with an exercise price of $4.25 per share. In accordance with
      SFAS No. 15,  Accounting  by  Debtors  and  Creditors  for  Troubled  Debt
      Restructurings,  the Company recorded an extraordinary  gain of $8,876,685
      related to the exchange.  The extraordinary gain represents the difference
      between the  carrying  value of the 9% Notes plus accrued  interest,  less
      $2,249,173 of deferred  financing costs written off, and the fair value of
      the Series A convertible  preferred  stock, as determined by the per share
      sales price of Series A convertible  preferred stock sold in the 1998 Unit
      Financing (see Note 15(c)),  and warrants to purchase  common stock issued
      by the Company.

(8)   G.D. SEARLE & CO. AGREEMENT

      In January 1996, the Company and G.D. Searle & Co. (Searle) entered into a
      collaboration   relating  to  research  and   development  of  therapeutic
      antisense compounds. According to the collaboration agreement, as modified
      in April 1998, targets can be selected from those in the fields of cancer,
      cardiovascular  disease  and  inflammation/immunomodulation   (the  Searle
      Field).

      Pursuant to the  collaboration,  the parties are  conducting  research and
      development  relating  to a compound  directed at MDM2.  In this  project,
      Searle is funding certain research and development efforts by the Company,
      and  both  Searle  and  the  Company  have  committed  certain  of its own
      personnel  to  the  collaboration.  The  initial  phase  of  research  and
      development  activities  will be conducted  through the earlier of (i) the
      achievement of certain  milestones,  and (ii) January 31, 2000, subject to
      early   termination  by  Searle.   The  parties  may  extend  the  initial
      collaboration by mutual  agreement,  including  agreement as to additional
      research funding by Searle.

      In addition, under the collaboration, Searle has the right to designate up
      to six additional  molecular  targets in the Searle Field (the  Additional
      Targets) on terms substantially consistent with the terms



                                      F-15



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



      of the  collaboration  applicable to the initial  molecular  target.  This
      right is  exercisable  by Searle  with  respect to each of the  Additional
      Targets upon the payment by Searle of certain  research  payments  (beyond
      the  project-specific  payments  relating  to  the  particular  Additional
      Target) and the  purchase of  additional  common stock from the Company by
      Searle (at the then fair market value). The aggregate amount to be paid by
      Searle  for such  research  payments  and  equity  investment  in order to
      designate  each of the Additional  Targets is  $10,000,000  per Additional
      Target. In the event that Searle designates all of the Additional Targets,
      the  aggregate  amount to be paid by Searle for research  payments will be
      $24,000,000,  and the  aggregate  amount  to be paid by  Searle  in equity
      investment  will be  $36,000,000.  If Searle has not designated all of the
      Additional  Targets by the time the  initial  molecular  target  reaches a
      certain  stage of  preclinical  development,  Searle  will be  required to
      purchase  an  additional  $10,000,000  of  common  stock (at the then fair
      market  value)  in order to  maintain  its right to  designate  any of the
      Additional  Targets.  The  payment  for  any  such  common  stock  will be
      creditable  against the equity  investment  portion of the  payments to be
      made by Searle with respect to the  designation  of any of the  Additional
      Targets that Searle has not yet designated.

      Searle has exclusive rights to commercialize  any products  resulting from
      the  collaboration.  If Searle elects to  commercialize a product,  Searle
      will fund and perform preclinical tests and clinical trials of the product
      candidate  and  will  be  responsible  for  regulatory  approvals  for and
      marketing of the product.  The Company has agreed to perform  research and
      development work exclusively  with Searle.  In addition,  for each product
      candidate,  the Company will be entitled to milestone payments from Searle
      totaling up to an aggregate of $10,000,000 upon the achievement of certain
      development  benchmarks.  The Company  also will be entitled to  royalties
      from net sales of products  resulting from the  collaboration.  Subject to
      satisfying certain conditions relating to its manufacturing capacities and
      capabilities,  the Company will retain  manufacturing  rights,  and Searle
      will be required to purchase its requirements of products from the Company
      on an exclusive basis at specified prices. Upon a change in control of the
      Company,   Searle  would  have  the  right  to  terminate   the  Company's
      manufacturing  rights,  although the royalty payable would be increased in
      such event.

      In the event that Searle  designates all of the  Additional  Targets or if
      Hybridon   fails  to  satisfy   certain   requirements   relating  to  its
      manufacturing  capacities and capabilities,  Searle will have the right to
      require  Hybridon to form a joint  venture  with Searle,  as defined.  The
      Company  and  Searle  would  each own 50% of the joint  venture,  although
      Searle's ownership interest in the joint venture would increase based upon
      a formula to up to a maximum of 75% if the joint venture is established in
      certain  instances  relating to the Company's  failure to satisfy  certain
      requirements relating to its manufacturing capacities and capabilities.

      During 1996,  1997 and 1998,  the Company  earned  $400,000,  $600,000 and
      $600,000,  respectively, in research and development revenues from Searle.
      Under the  collaboration,  Searle also purchased  200,000 shares of common
      stock in the Company at the offering price of $50.00 per share.



                                      F-16



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



(9)   F. HOFFMANN-LA ROCHE LTD. (ROCHE) COLLABORATION

      In  December  1992,  the Company and Roche  entered  into a  collaboration
      involving  the  application  of the  Company's  antisense  oligonucleotide
      chemistry to develop compounds for the treatment of hepatitis B, hepatitis
      C and human  papilloma  virus.  On September 3, 1997,  Roche  notified the
      Company that it had decided not to pursue further  collaboration  with the
      Company and was terminating the collaboration effective February 28, 1998.

      The  Company  has  recorded   $1,019,389  and  $345,000  of  research  and
      development  revenue  related  to this  collaboration  in 1996  and  1997,
      respectively.  Due to the termination of the  collaboration,  as discussed
      above,   the  Company   recognized   no  revenue   with  respect  to  this
      collaboration in 1998.

(10)  MEDTRONIC, INC. COLLABORATIVE STUDY AGREEMENT

      In May 1994, the Company and Medtronic,  Inc.  (Medtronic)  entered into a
      collaborative  study  agreement  (the Medtronic  Agreement)  involving the
      development  of  antisense  compounds  for the  treatment  of  Alzheimer's
      disease and a drug  delivery  system to deliver  such  compounds  into the
      central  nervous  system.  The  agreement  provides  that the  Company  is
      responsible  for the  development  of,  and hold all  rights  to, any drug
      developed pursuant to this collaboration, and Medtronic is responsible for
      the development of, and hold all rights to, any delivery system  developed
      pursuant to this collaboration.  The parties may extend this collaboration
      by  mutual  agreement  to other  neurodegenerative  disease  targets.  The
      Company  is  not   currently   conducting   any   activities   under  this
      collaboration.

(11)  LICENSING AGREEMENT

      The Company has entered  into a  licensing  agreement  with the  Worcester
      Foundation  for  Biomedical  Research,  Inc.,  which has  merged  with the
      University of  Massachusetts  Medical Center,  under which the Company has
      received  exclusive  licenses to certain patents and patent  applications.
      The Company is required to make royalty  payments based on future sales of
      products  employing the technology or falling under claims of a patent, as
      well as a specified  percentage of sublicense  income received  related to
      the licensed technology.  Additionally,  the Company is required to pay an
      annual maintenance fee through the life of the patents.

(12)  PHARMACIA BIOTECH, INC. COLLABORATION

      In December  1994,  the Company and Pharmacia  Biotech,  Inc.  (Pharmacia)
      entered into a  collaboration  involving the design and  development  of a
      large-scale oligonucleotide synthesis machine. Following completion of the
      machine  in  December  1996,  the  collaboration  expired,  and  Pharmacia
      retained  the right to sell the  machine to third  parties,  subject to an
      obligation to pay the Company royalties on such third-party sales.  During
      1996 and 1997, the Company received $62,321 and $48,000,  respectively, of
      royalty income related to such third-party  sales. The Company  recognized
      no royalty income related to this collaboration for 1998.



                                      F-17



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



(13)  PERKIN-ELMER CORPORATION SALES AND SUPPLY AGREEMENT

      In  September  1996,  the Company and the Applied  Biosystems  Division of
      Perkin-Elmer  Corporation  (Perkin-Elmer)  signed a  four-year  sales  and
      supply  agreement  under  which  Perkin-Elmer  agreed  to refer  potential
      customers to HSP for the  manufacture of custom  oligonucleotides  and the
      Company agreed that amidites for the manufacture of these oligonucleotides
      would be purchased from  Perkin-Elmer  and a percentage of the sales price
      will be paid to Perkin-Elmer.  In addition,  Perkin-Elmer  licensed to the
      Company its oligonucleotide synthesis patents.

(14) INVESTMENT IN METHYLGENE, INC.

      In January 1996,  the Company and three Canadian  institutional  investors
      formed a Quebec  company,  MethylGene,  Inc.  (MethylGene)  to develop and
      market  certain  compounds and procedures to be agreed upon by the Company
      and MethylGene.

      The Company has granted to  MethylGene  exclusive  worldwide  licenses and
      sublicenses  in respect of certain  technology  relating to the MethylGene
      fields.  These fields, as amended,  are defined as (i) antisense compounds
      to inhibit DNA  methyltransferase  for the treatment of any disease;  (ii)
      other methods of inhibiting DNA methyltransferase for the treatment of any
      disease;  and (iii)  antisense  compounds to inhibit up to two  additional
      molecular  targets for the treatment of cancers,  to be agreed upon by the
      Company and  MethylGene.  In  addition,  the Company and  MethylGene  have
      entered into a supply agreement  pursuant to which MethylGene is obligated
      to purchase from the Company all required formulated bulk oligonucleotides
      at specified transfer prices.

      The  Company  acquired a 49%  interest  in  MethylGene  for  approximately
      $734,000, and the Canadian investors acquired a 51% interest in MethylGene
      for a total of approximately $5,500,000.  The institutional investors have
      the right to exchange all (but not less than all) of their shares of stock
      in MethylGene for an aggregate of 100,000 shares of Hybridon  common stock
      (subject to adjustment  for stock splits,  stock  dividends and the like).
      This option is exercisable  only during a 90-day period  commencing on the
      earlier of the date five  years  after the  closing  of the  institutional
      investors' investment in MethylGene or the date on which MethylGene ceases
      operations.  This option  terminates  sooner if MethylGene  raises certain
      additional  amounts of equity or debt  financing or if  MethylGene  enters
      into a corporate  collaboration  that meets certain  requirements.  During
      1998,  MethylGene raised  additional  proceeds from outside investors that
      decreased the Company's interest to 30%. The Company is accounting for its
      investment in MethylGene under the equity method and, due to the existence
      of the investors  exchange  rights,  the Company has  recorded,  up to its
      original  investment,  100% of  MethylGene's  losses  in the  accompanying
      consolidated statement of operations.

      In  May  1998,   this   agreement  was  amended  to  grant   MethylGene  a
      non-exclusive right to use any and all antisense chemistries discovered by
      the Company or any of its  affiliates  for a period  commencing  on May 5,
      1998 and ending on the earlier of (i) the effective date of termination by
      MethylGene of its contract for development  services to be provided by the
      Company; (ii) May 5,



                                      F-18



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



      1999, unless MethylGene  exercises its option to continue  contracting for
      development  services  provided by the Company;  or (iii) May 5, 2000.  As
      additional  consideration  for  this  nonexclusive  right,  MethylGene  is
      required to pay the Company certain  milestone  amounts,  as defined,  and
      transferred  300,000 shares of MethylGene's Class B shares to the Company.
      The Company has placed no value on these  shares.  During  1996,  1997 and
      1998,   the  Company   recognized   $49,565,   $101,894  and   $1,685,932,
      respectively, of product and service revenue related to this agreement.

(15)  STOCKHOLDERS' EQUITY (DEFICIT)

      (a)  Common Stock

      The Company has 100,000,000  authorized shares of common stock,  $.001 par
      value, of which 15,304,825  shares were issued and outstanding at December
      31, 1998.

      (b)  Initial Public Offering (IPO)

      On February 2, 1996, the Company  completed its IPO of 1,150,000 shares of
      common stock at $50.00 per share. The sale of common stock resulted in net
      proceeds to the Company of $52,231,244 after deducting expenses related to
      the offering.

      (c)  1998 Unit Financing

      On May 5,  1998,  the  Company  completed  a  private  offering  of equity
      securities  raising total gross proceeds of $26,681,164  from the issuance
      of  9,597,476  shares  of  common  stock,   114,285  shares  of  Series  A
      convertible  preferred stock and warrants to purchase  3,329,486 shares of
      common stock at $2.40 per share. The gross proceeds include the conversion
      of $5,934,558 of accounts  payable,  capital lease  obligations  and other
      obligations  into common stock.  The Company  incurred  $1,636,137 of cash
      expenses  related to the private  offering  and issued  597,699  shares of
      common stock and warrants to purchase  1,720,825 shares of common stock at
      $2.40 per share to the  placement  agents.  The  compensation  received by
      Pillar, a company  affiliated with certain directors of the Company,  with
      respect  to the  offshore  component  of the  private  offering  (Offshore
      Offering) consisted of (i) 9% of gross proceeds of such Offshore Offerings
      and (ii) a nonaccountable  expense allowance equal to 4% of gross proceeds
      of such Offshore  Offering.  Pillar  received  $1,636,137  and warrants to
      purchase 1,111,630 shares of common stock at $2.40 per share.

      In addition,  Pillar is entitled to receive 300,000 shares of common stock
      in connection  with its efforts in assisting the Company in  restructuring
      its  balance  sheet.  The  Company  has  recorded  $600,000 of general and
      administrative  expense  in the  accompanying  consolidated  statement  of
      operations during 1998, which represents the value of this common stock on
      May 5, 1998 with an offsetting  amount to accrued  expenses for the shares
      to be issued. These shares will be issued in 1999.




                                      F-19



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



      (d)  Units Issued to Primedica Corporation

      In connection  with the unit financing (see Note 15(c)) the Company issued
      250,000  shares of common  stock and 62,500  warrants to  purchase  common
      stock to  Primedica  Corporation  (Primedica)  for future  services  to be
      provided. The services shall commence upon the Company's request after (i)
      the Company's  securities are listed on a nationally  recognized exchange,
      and (ii) the average  closing  price of the  Company's  common stock is at
      least $2.00 per share for the  twenty-day  trading  period  preceding  the
      contract  commencement  date.  In the event that the Company  does not use
      these services as a result of the failure to meet the contract conditions,
      Primedica shall forfeit to the Company all or part of the common stock and
      warrants  held by  Primedica.  The Company has  recorded  these  shares as
      issued and outstanding at December 31, 1998 at par value. The Company will
      record the value of these services as the services are rendered.

      (e)  Stock Split

      On December  10,  1997,  the Board of  Directors  declared a  one-for-five
      reverse split of its common stock.  Share quantities and related per share
      amounts  have been  retroactively  restated to reflect  the reverse  stock
      split.

      (f)  Warrants

      The Company has the following warrants outstanding and exercisable for the
      purchase of common stock at December 31, 1998:

<TABLE>
<CAPTION>
                                            Outstanding    Exercise Price     Exercisable    Exercise Price
    Expiration Date                           Warrants         per Share        Warrants         per Share
    ---------------                           --------         ---------        --------         ---------

<S>                                            <C>               <C>             <C>               <C>   
    February 4, 1999-October 25, 2000          551,201           $50.00          551,201           $50.00
    February 28, 2000                           20,000            37.50           20,000            37.50
    December 31, 2001                           13,000            34.49           13,000            34.49
    May 4, 2003                              8,641,503        2.40-4.25        4,378,044             2.40
                                       ---------------                   ---------------

                                             9,225,704                         4,962,245   
                                       ===============                   ===============

    Weighted average exercise price                               $5.48                             $7.91
    per share                                                     =====                             =====

</TABLE>


      Five-year  warrants to purchase  368,620  shares of common stock at $50.00
      per share were issued in 1994 and 1995 as a component of the  compensation
      for  services of several  placement  agents of the  Company's  convertible
      preferred stock. Of these warrants,  304,335 were issued to a company that
      is  controlled  by two  directors  of the Company  (see Note  16(b)).  The
      remaining  64,285  warrants  were issued to various other  companies  that
      acted as  placement  agents.  See Note 15(c) for  information  relating to
      warrants  issued  to  placement  agents in  connection  with the 1998 Unit
      Financing.




                                      F-20



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



      As  consideration  of the  agreements  made  by  Forum  consenting  to the
      Company's 1998 private  placements and waiving certain  obligations of the
      Company to Forum,  the  Company  agreed to amend the  warrant to  purchase
      71,301  shares of common  stock at an exercise  price of $35.06 per share,
      issued to Forum in  connection  with 9% notes so that the  exercise  price
      will be equal to $4.25 per share, and the number of shares of common stock
      purchasable  upon exercise  thereof will be increased to 588,235,  in each
      case subject to adjustment; provided, however, that such warrant will also
      be amended to provide that such warrant may not be exercised  until May 5,
      1999 and the transactions  contemplated by such private  placements and by
      the exchange offer will not trigger any  anti-dilution  adjustments to the
      exercise  price  thereof or the number of shares of common  stock  subject
      thereto.

      (g)  Stock Options

      In 1990 and 1995, the Company  established the 1990 Stock Option Plan (the
      1990 Option Plan) and the 1995 Stock  Option Plan (the 1995 Option  Plan),
      respectively,  which provide for the grant of incentive  stock options and
      nonqualified  stock options.  Options  granted under these plans vest over
      various  periods and expire no later than 10 years from the date of grant.
      However,  under the 1990 Option Plan,  in the event of a change in control
      (as  defined in the 1990 Plan),  the  exercise  dates of all options  then
      outstanding   shall  be  accelerated  in  full  and  any  restrictions  on
      exercising  outstanding  options  issued  pursuant to the 1990 Option Plan
      shall terminate.  In October 1995, the Company  terminated the issuance of
      additional  options  under the 1990 Option Plan.  As of December 31, 1998,
      options to  purchase a total of 525,638  shares of common  stock  remained
      outstanding under the 1990 Option Plan.

      A total of 700,000  shares of common stock may be issued upon the exercise
      of options  granted  under the 1995 Option  Plan.  The  maximum  number of
      shares with respect to which options may be granted to any employee  under
      the 1995  Option  Plan shall not  exceed  500,000  shares of common  stock
      during any  calendar  year.  The  Compensation  Committee  of the Board of
      Directors  has the  authority to select the  employees to whom options are
      granted and determine  the terms of each option,  including (i) the number
      of shares of common  stock  subject  to the  option;  (ii) when the option
      becomes  exercisable;  (iii) the option exercise price, which, in the case
      of  incentive  stock  options,  must be at least 100% (110% in the case of
      incentive stock options  granted to a stockholder  owning in excess of 10%
      of the  Company's  common  stock) of the fair  market  value of the common
      stock as of the date of grant; and (iv) the duration of the option (which,
      in the case of incentive  stock options,  may not exceed 10 years).  As of
      December 31, 1998, options to purchase a total of 550,534 shares of common
      stock remained outstanding under the 1995 Option Plan.

      In October 1995,  the Company  adopted the 1995 Director Stock Option Plan
      (the  Director  Plan).  A total of 50,000  shares  of common  stock may be
      issued upon the exercise of options granted under the Director Plan. Under
      the terms of the Director Plan, options to purchase 1,000 shares of common
      stock were granted to eligible directors upon the closing of the Company's
      initial  public  offering at the fair market  value of the common stock on
      the date of the closing.  Thereafter,  options to purchase 1,000 shares of
      common stock will be granted to each eligible director on



                                      F-21



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



      May 1 of each year  commencing in 1997. All options will vest on the first
      anniversary  of the date of grant or, in the case of  annual  options,  on
      April 30 of each year with  respect  to options  granted  in the  previous
      year.  As of  December  31,  1998,  options to  purchase a total of 21,000
      shares of common stock remained outstanding under the Director Plan.

      In May 1997,  the  Company  adopted  the 1997 Stock  Option Plan (the 1997
      Option Plan) and has reserved and may issue up to 4,500,000 shares for the
      grant of incentive and nonqualified  stock options.  The maximum number of
      shares with respect to which options may be granted to any employee  under
      the 1997  Option  Plan shall not  exceed  500,000  shares of common  stock
      during any  calendar  year.  The  Compensation  Committee  of the Board of
      Directors  has the  authority to select the  employees to whom options are
      granted and determine  the terms of each option,  including (i) the number
      of shares of common  stock  subject  to the  option;  (ii) when the option
      becomes  exercisable;  (iii) the option exercise price, which, in the case
      of  incentive  stock  options,  must be at least 100% (110% in the case of
      incentive  stock) of the fair market  value of the common  stock as of the
      date of grant; and (iv) the duration of the option (which,  in the case of
      incentive  stock  options,  may not exceed ten years).  As of December 31,
      1998,  options to  purchase a total of  2,363,560  shares of common  stock
      remained outstanding under the 1997 Option Plan.

      Stock  option  activity  for the three  years ended  December  31, 1998 is
      summarized as follows:

<TABLE>
<CAPTION>

                                                                                                                      Weighted
                                                                             Number         Exercise Price         Average Price 
                                                                            of Shares          per Share              per Share

<S>               <C>                                                       <C>           <C>                           <C>    

                    Outstanding, December 31, 1995                               738,208   $  .01  - $ 50.00            $29.15
                             Granted                                             476,020    25.00  -   65.60             49.55
                             Exercised                                           (57,740)     .01  -   37.50             18.85
                             Terminated                                          (20,100)   25.00  -   57.85             40.20
                                                                                 -------

                    Outstanding, December 31, 1996                             1,136,388     1.25  -   65.60             38.05
                             Granted                                             315,675    27.50  -   32.50             30.75
                             Exercise                                            (25,005)    1.25  -   40.00             12.60
                             Terminated                                         (236,561)    2.50  -   65.60             40.35
                                                                               ---------

                    Outstanding, December 31, 1997                             1,190,497     1.25  -   65.60             36.18
                             Granted                                           2,513,000     2.00  -    3.13              2.00
                             Terminated                                        (242,765)     2.50  -   57.85             37.79
                                                                               --------

                    Outstanding, December 31, 1998                             3,460,732    $1.25  -  $65.60             $11.25
                                                                               =========    ================             ======

                    Exercisable, December 31, 1996                               622,930    $1.25  -  $65.60             $32.55
                                                                               =========    ================             ======

                    Exercisable, December 31, 1997                               740,780    $1.25  -  $65.60             $34.40
                                                                               =========    ================             ======

                    Exercisable, December 31, 1998                             1,650,021    $1.25     $65.60             $17.13
                                                                               =========    ================             ======

</TABLE>





                                      F-22



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)

<TABLE>
<CAPTION>


                               Options Outstanding               Options Exercisable

                                      Weighted       Weighted                      Weighted
                                       Average        Average                       Average
                                      Remaining      Exercise                      Exercise
Range of Exercise       Number       Contractual     Price per       Number        Price per
      Prices          Outstanding       Life           Share       Outstanding       Share
<S>                   <C>            <C>             <C>           <C>             <C>

$          1.25             10,000      3.10           $  1.25           10,000     $    1.25
  2.00  -  2.37          2,505,000      9.56              2.00          901,562          2.00
  2.44  -  3.13             18,800      6.03              2.61           10,800          2.50
  4.25  -  5.00              1,200      3.75              5.00            1,200          3.75
 17.50  -  25.00           197,330      3.54             23.21          191,331         23.15
 27.50  -  31.66           168,974      7.45             30.50           76,017         30.28
 35.00  -  36.25            30,000      6.73             35.71           30,000         35.71
 37.50  -  37.50           316,048      4.72             37.50          282,583         37.50
 38.13  -  43.75            47,900      7.81             40.64           24,648         40.73
           50.00            17,700      6.35             50.00           11,700         50.00
 57.85  -  65.60           147,780      6.08             58.22          110,180         58.34
                     -------------                                -------------

                         3,460,732                    $  11.25        1,650,021        $17.13
                     =============                    ========    =============        ======

</TABLE>

        In  October  1995,  the  FASB  issued  SFAS  No.  123,   Accounting  for
        Stock-Based  Compensation.  SFAS No. 123 requires the measurement of the
        fair value of stock  options or  warrants  granted  to  employees  to be
        included in the  statement  of  operations  or disclosed in the notes to
        financial  statements.  The Company has determined that it will continue
        to account for stock-based  compensation  for employees under Accounting
        Principles   Board   Opinion  No.  25  and  elect  the   disclosure-only
        alternative  under SFAS No.  123.  In 1996,  1997 and 1998,  the Company
        recorded $1,967,116,  $205,978 and $109,734,  respectively,  of deferred
        compensation  related to grants to  nonemployees,  net of  terminations.
        Deferred  compensation  will be amortized over the vesting period of the
        options.  The Company has  recorded  compensation  expense of  $763,190,
        $316,067 and $246,444 in 1996, 1997 and 1998,  respectively,  related to
        these grants to nonemployees.

        The Company has computed the pro forma  disclosures  require by SFAS No.
        123 for all stock  options  granted  after  January  1,  1995  using the
        Black-Scholes  option pricing model.  The assumptions used for the three
        years ended December 31, 1998 are as follows:

<TABLE>
<CAPTION>

                                              1996            1997            1998
<S>          <C>                           <C>              <C>               <C>    

             Risk free interest rate         6.14%            6.22%           5.15%
             Expected dividend yield           -                -               -
             Expected lives                 6 years          6 years         6 years
             Expected volatility              60%              60%             60%

</TABLE>

        The  Black-Scholes  option  pricing  model  was  developed  for  use  in
        estimating  the fair  value of  traded  options  which  have no  vesting
        restrictions  and are fully  transferable.  In addition,  option pricing
        models  require  the input of highly  subjective  assumptions  including
        expected stock price



                                      F-23



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



        volatility.   Because  the   Company's   employee   stock  options  have
        characteristics  significantly  different from those of traded  options,
        and because changes in the subjective  input  assumptions can materially
        affect the fair value estimate,  in management's  opinion,  the existing
        models do not necessarily  provide a reliable single measure of the fair
        value of its employee stock options.

        The effect of applying  SFAS No. 123 for the three years ended  December
        31, 1998 would be as follows:

<TABLE>
<CAPTION>
                                                         1996               1997                1998
<S>                                              <C>                <C>                <C>              
     Net loss applicable to common
     stockholders-
       As reported                               $    (46,852,600)  $    (69,461,326)  $    (19,792,736)
                                                 =================  =================  =================
       Pro forma                                 $    (52,890,455)  $    (73,402,170)  $    (23,131,304)
                                                 =================  =================  =================
     Basic and Diluted net loss per common
     shares-
       As reported                                        $(10.24)           $(13.76)             $(1.67)
                                                          =======            ========             =======
       Pro forma                                          $(11.56)           $(14.54)             $(1.95)
                                                          =======            ========             =======
</TABLE>


        (h)    Employee Stock Purchase Plan

        In October 1995,  the Company  adopted the 1995 Employee  Stock Purchase
        Plan (the  Purchase  Plan),  under which up to 100,000  shares of common
        stock  may be issued  to  participating  employees  of the  Company,  as
        defined, or its subsidiaries.

        On the first day of a designated  payroll deduction period (the Offering
        Period),  the  Company  will  grant to each  eligible  employee  who has
        elected to participate in the Purchase Plan an option to purchase shares
        of common  stock as follows:  the  employee  may  authorize an amount (a
        whole  percentage from 1% to 10% of such  employee's  regular pay) to be
        deducted by the Company from such pay during the Offering Period. On the
        last  day of the  Offering  Period,  the  employee  is  deemed  to  have
        exercised the option,  at the option  exercise  price,  to the extent of
        accumulated  payroll  deductions.  Under the terms of the Purchase Plan,
        the option  price is an amount equal to 85% of the fair market value per
        share of the common stock on either the first day or the last day of the
        Offering  Period,  whichever  is  lower.  In no  event  may an  employee
        purchase  in any one  Offering  Period a number of shares  which is more
        than 15% of the  employee's  annualized  base pay  divided by 85% of the
        market value of a share of common stock on the commencement  date of the
        Offering  Period.  The  Compensation  Committee may, in its  discretion,
        choose an Offering Period of 12 months or less for each of the Offerings
        and choose a different Offering Period for each Offering. No shares have
        been issued under the Plan.

        (i)    Preferred Stock

        The restated  Certificate of  Incorporation  of the Company  permits its
        Board of Directors to issue up to 5,000,000  shares of preferred  stock,
        par value $.01 per share (the Preferred  Stock),  in one or more series,
        to designate the number of shares  constituting such series,  and fix by
        resolution,



                                      F-24



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



        the powers,  privileges,  preferences and relative,  optional or special
        rights thereof,  including  liquidation  preferences and dividends,  and
        conversion and redemption  rights of each such series.  During 1998, the
        Company  designated  1,500,000 shares as Series A convertible  preferred
        stock.

        (j)    Series A Convertible Preferred Stock

        The rights and  preferences of the Series A convertible  preferred stock
        are as follows:

               Dividends

               The holders of the Series A convertible  preferred  stock,  as of
               March 15 or  September  15, are  entitled  to  receive  dividends
               payable at the rate of 6.5% per annum,  payable  semi-annually in
               arrears. Such dividends shall accrue from the date of issuance of
               such share and shall be paid semi-annually on April 1 and October
               1 of each year.  Such dividends shall be paid, at the election of
               the Company, either in cash or additional duly authorized,  fully
               paid and non assessable shares of Series A convertible  preferred
               stock.   In  calculating   the  number  of  shares  of  Series  A
               convertible  preferred  stock  to be paid  with  respect  to each
               dividend,  the  Series A  convertible  preferred  stock  shall be
               valued at $100.00 per share.  During 1998, the Company recorded a
               total  accretion  of  $2,689,048  for the  dividend  on  Series A
               preferred  stock and issued 16,470 shares of Series A convertible
               preferred stock as a dividend.

               Liquidation

               In the event of a  liquidation,  dissolution or winding up of the
               Company,  whether  voluntary  or  involuntary,  after  payment or
               provision  for  payment  of debts  and other  liabilities  of the
               Company,  the holder of the Series A convertible  preferred stock
               then  outstanding  shall be entitled to be paid out of the assets
               of the Company available for distribution to its stockholders, an
               amount  equal to $100.00  per share plus all  accrued  but unpaid
               dividends.  If the assets to be distributed to the holders of the
               Series A convertible  preferred  stock shall be  insufficient  to
               permit the  payment of the full  preferential  amounts,  then the
               assets of the Company shall be distributed ratably to the holders
               of the Series A convertible  preferred  stock on the basis of the
               number of shares of Series A  convertible  preferred  stock held.
               All shares of Series A convertible  preferred stock shall rank as
               to payment upon the occurrence of any liquidation event senior to
               the common stock.

               Conversion

               Commencing  after May 6, 1999, but not prior thereto,  the shares
               of Series A convertible preferred stock shall be convertible,  in
               whole or in part, at the option of the holder into fully paid and
               nonassessable  shares of common stock at $4.25 per share, subject
               to adjustment as defined.



                                      F-25



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



               Mandatory Conversion

               At any time after May 6, 1998,  the  Company at its  option,  may
               cause the Series A convertible preferred stock to be converted in
               whole  or in part,  on a pro  rata  basis,  into  fully  paid and
               nonassessable  shares of common  stock using a  conversion  price
               equal to $4.00 if the  closing  bid  price,  as  defined,  of the
               common  stock  shall  have  equaled  or  exceeded   250%  of  the
               conversion price, $4.25, subject to adjustment as defined, for at
               least 20 trading  days in any 30  consecutive  trading day period
               ending three days prior to the date of notice of conversion (such
               event, the Market Trigger).

               At any time after April 1, 2000, the Company,  at its option, may
               redeem the Series A convertible preferred stock for cash equal to
               $100.00 per share plus all accrued and unpaid  dividends  at such
               time,  if the Market  Trigger has  occurred in the period  ending
               three days prior to the date of notice of redemption.

(16)    COMMITMENTS AND CONTINGENCIES

        (a)    Facilities

               The Company leases its facility in Milford, Massachusetts,  under
               a lease  which has a 10- year term,  which  commenced  on July 1,
               1994, with certain extension options.

               On February 4, 1994, the Company entered into the Cambridge Lease
               with a partnership  that is affiliated with certain  directors of
               the  Company.  As  compensation  for  arranging  this lease,  the
               Company issued Pillar Limited five-year warrants for the purchase
               of 100,000  shares of the  Company's  common stock at an exercise
               price of $50.00 per share.  These warrants expired  subsequent to
               December   31,   1998.   The  Company   vacated  the   Cambridge,
               Massachusetts,  facility  in June 1998 and  moved  its  corporate
               facilities to Milford, Massachusetts (see Note 3).

               Future approximate minimum rent payments as of December 31, 1998,
               under  existing  lease  agreements  through 2007, net of sublease
               agreements are as follows:

          December 31,                       Amount
          ------------                       ------

          1999                          $       614,000
          2000                                  784,000
          2001                                1,213,000
          2002                                1,209,000
          2003                                1,213,000
          Thereafter                          2,338,000
                                        ---------------
                                        $     7,371,000
                                        ===============




                                      F-26



<PAGE>


                                HYBRIDON, INC. AND SUBSIDIARIES



                          NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                       DECEMBER 31, 1998



                                          (Continued)



        During  1996,  1997 and 1998,  facility  rent  expense  net of  sublease
        revenue  was  approximately   $2,352,000,   $4,613,000  and  $3,871,000,
        respectively.

        (b)    Related-Party  Agreements  with  Affiliates of  Stockholders  and
               Directors

               The  Company  has  entered  into  consulting  agreements,   stock
               placement  agreements  and an  advisory  agreement  with  several
               companies that are controlled by two  shareholders  and directors
               of the Company  including  Forum,  S.A.  Pillar  Investment  N.V.
               (Pillar Investment), Pillar S.A. (formerly Commerce Consult S.A.)
               and Pillar Investment  Limited (formerly Ash Properties  Limited)
               (Pillar  Limited).  During 1996,  1997 and 1998,  the Company had
               expensed $1,106,000, $998,000 and $1,300,000, respectively, under
               consulting and advisory agreements with related parties.

        (c)    Other Research and Development Agreements

               The Company has entered into  consulting and research  agreements
               with the  universities,  research and testing  organizations  and
               individuals,  under  which  consulting  and  research  support is
               provided to the Company.  These  agreements are for varying terms
               and  provide  for  certain  minimum  annual or per diem fees plus
               reimbursable  expenses  to be paid during the  contract  periods.
               Future minimum fees payable under these  contracts as of December
               31, 1998 are approximately as follows:

                December 31,                   Amount
                ------------                   ------

                1999                      $       582,000
                2000                              392,000
                2001                              279,000
                                          ---------------
                                          $     1,253,000
                                          ===============

               Total fees and expenses under these contracts were  approximately
               $7,171,000, $9,372,000 and $2,011,000 during 1996, 1997 and 1998,
               respectively.

        (d)    Employment Agreements

               The Company  has  entered  into  employment  agreements  with its
               executive  officers which provide for,  among other things,  each
               officer's  annual  salary,  cash  bonus,  fringe  benefits,   and
               vacation and severance  arrangements.  Under the agreements,  the
               officers are generally  entitled to receive severance payments of
               two to three year's base salary.


                                      F-27



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



        (e)    Contingencies

               From time to time, the Company may be exposed to various types of
               litigation.  The Company is not engaged in any legal  proceedings
               that are expected,  individually  or in the aggregate,  to have a
               material adverse effect on the Company's  financial  condition or
               results of operations.

(17)    INCOME TAXES

        The  Company  applies  SFAS No. 109,  Accounting  for Income  Taxes.  At
        December 31,  1998,  the Company had net  operating  loss and tax credit
        carryforwards   for  federal   income  tax  purposes  of   approximately
        $219,993,000 and $3,936,000,  respectively,  available to reduce federal
        taxable  income and federal income taxes,  respectively.  The Tax Reform
        Act of 1986 (the Act), enacted in October 1986, limits the amount of net
        operating  loss and credit  carryforwards  that companies may utilize in
        any one year in the event of  cumulative  changes  in  ownership  over a
        three-year  period in excess of 50%. The Company has  completed  several
        financings  since the effective date of the Act,  which,  as of December
        31,  1998,  have  resulted  in  ownership  changes in excess of 50%,  as
        defined  under the Act and which  will  limit the  Company's  ability to
        utilize  its net  operating  loss  carryforwards.  Ownership  changes in
        future periods may place additional  limits on the Company's  ability to
        utilize net operating loss and tax credit carryforwards.

        The   federal  net   operating   loss   carryforwards   and  tax  credit
        carryforwards expire approximately as follows:

                                         Net                   
                                    Operating Loss              Tax Credit  
              Expiration Date       Carryforwards              Carryforwards
              ---------------       -------------              -------------

              December 31,
                  2005             $    666,000             $     15,000
                  2006                3,040,000                   88,000
                  2007                7,897,000                  278,000
                  2008               18,300,000                  627,000
                  2009               25,670,000                  689,000
                  2010               36,134,000                  496,000
                  2011               44,947,000                  493,000
                  2012               60,087,000                  750,000
                  2018               23,252,000                  500,000
                                   ------------             ------------

                                   $219,993,000             $  3,936,000
                                   ============             ============



                                      F-28



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)



        At December 31, 1997 and 1998, the components of the deferred tax assets
        are approximately as follows:

                                                    1997                1998
                                                    ----                ----

  Operating loss carryforwards                $ 78,696,000       $ 87,997,000
  Temporary differences                          5,137,000          2,677,000
  Tax credit carryforwards                       3,436,000          3,936,000
                                              ------------       ------------

                                                87,269,000         94,610,000

  Valuation allowance                          (87,269,000)       (94,610,000)
                                              ------------       ------------

                                              $          -       $          -
                                              ============       ============


        A valuation  allowance has been provided,  as it is more likely than not
        the Company will not realize the  deferred tax asset.  The net change in
        the  total   valuation   allowance   during  1998  was  an  increase  of
        approximately $7,341,000.

(18)    EMPLOYEE BENEFIT PLAN

        On October 10, 1991, the Company adopted an employee  benefit plan under
        Section 401(k) of the Internal  Revenue Code. The plan allows  employees
        to  make   contributions   up  to  a  specified   percentage   of  their
        compensation.  Under the plan, the Company may, but is not obligated to,
        match a portion of the employees' contributions up to a defined maximum.
        The Company is currently  matching 50% of employee  contributions to the
        plan,  up to 6% of the  employee's  annual base  salary,  and charged to
        operations  approximately  $224,000,  $253,000 and $253,000 during 1996,
        1997 and 1998, respectively.

(19)    SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION

        Supplemental  disclosure of cash flow information for the three years in
        the period ended December 31, 1998 are as follows:


<TABLE>
<CAPTION>
                                                                                        1996                1997               1998

<S>                                                                              <C>                 <C>                 <C>        
Cash paid during the period for interest                                         $      124,052      $    3,264,596      $ 1,666,127
                                                                                 ==============      ==============      ===========
Purchase of property and equipment under capital leases                          $    1,722,333      $    2,374,502    $           -
                                                                                 ==============      ==============      ===========
Conversion of preferred stock into common stock                                  $      159,822       $           -    $           -
                                                                                 ==============      ==============      ===========
Deferred compensation related to grants of stock options to                      $    1,967,116      $      205,978      $   109,734
  nonemployees, net of terminations                                              ==============      ==============      ===========




                                      F-29



<PAGE>

                         HYBRIDON, INC. AND SUBSIDIARIES

                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

                                DECEMBER 31, 1998

                                   (Continued)


Issuance of Series A convertible preferred stock and attached                     $           -       $           -      $51,055,850
  warrants in exchange for conversion of 9% convertible                          ==============      ==============      ===========
  subordinated notes payable and accrued interest

Accretion of Series A convertible preferred stock dividends                       $           -       $           -      $ 2,689,048
                                                                                 ==============      ==============      ===========

Issuance of common stock and attached warrants in exchange                        $           -       $           -      $ 4,800,000
  for conversion of convertible promissory notes payable                         ==============      ==============      ===========

Issuance of common stock and attached warrants in exchange                        $           -       $           -      $ 5,934,558
  for conversion of accounts payable and other obligations                        ==============      ==============     ===========

</TABLE>


(20)    RESTATEMENT

        In March 1999, the Company  restated its June 30, 1998 and September 30,
        1998  financial  statements  to reflect  the  accretion  on the Series A
        convertible   preferred  stock,  and  record  $600,000  of  general  and
        administrative  expense  for the  300,000  shares of common  stock  that
        Pillar  is  entitled  to  receive  in  connection  with its  efforts  in
        assisting the Company in restructuring its balance sheet.

(21) ORIGENIX TECHNOLOGIES, INC.

        In January 1999, the Company and certain institutional  investors formed
        a Montreal company,  OriGenix  Technologies Inc. (OriGenix),  to develop
        and market drugs for the treatment of infectious diseases.

        The Company  received a 49%  interest in  OriGenix in  consideration  of
        certain research and development  efforts  previously  undertaken by the
        Company  which were made  available  to  OriGenix.  The Company has also
        licensed certain  antisense  compounds and other technology to OriGenix.
        If certain  conditions  are  satisfied  by OriGenix,  the  institutional
        investors are committed to make an additional investment,  at which time
        the  Company's  ownership  interest in OriGenix will be reduced 40%. The
        institutional  investors acquired a 51% interest in OriGenix for a total
        of  approximately  $4.0  million.  The  Company  will  account  for  its
        investment in OriGenix under the equity method.



                                      F-30


<PAGE>

                                  EXHIBIT INDEX

Exhibit No.           Description
- -----------           -----------


3.1(1)      Restated Certificate of Incorporation of the Registrant, as amended.

3.2(2)      Amended and Restated By-Laws of the Registrant.

3.3(3)      Form of Certificate of Designation of Series A Preferred Stock.

3.4(3)      Form of Certificate of Designation of Series B Preferred Stock.

4.1(2)      Specimen Certificate for shares of Common Stock, $.001 par value, of
            the Registrant.

4.2(4)      Indenture  dated as of March 26, 1997 between Forum Capital  Markets
            LLC and the Registrant.

4.3(7)      Certificate of Designation  of Series A Preferred  Stock,  par value
            $.01 per share, dated May 5, 1998.

4.4(7)      Class A Warrant Agreement dated May 5, 1998.

4.5(7)      Class B Warrant Agreement dated May 5, 1998.

4.6(7)      Class C Warrant Agreement dated May 5, 1998.

4.7(7)      Class D Warrant Agreement dated May 5, 1998.

+10.1(2)    License  Agreement  dated  February  21,  1990  and  restaged  as of
            September  8,  1993  between  the   Registrant   and  the  Worcester
            Foundation for Biomedical Research, Inc., as amended.

+10.2(2)    Patent  License  Agreement  dated  September  21,  1995  between the
            Registrant and National Institutes of Health.

+10.3(2)    Patent  License  Agreement  effective as of October 13, 1994 between
            the Registrant and McGill University.

+10.4(2)    License  Agreement  effective  as of October  25,  1995  between the
            Registrant and the General Hospital Corporation.

+10.5(2)    License   Agreement  dated  as  of  October  30,  1995  between  the
            Registrant and Yoon S. Cho-Chung.

+10.6(2)    Collaborative  Study  Agreement  effective  as of December  30, 1992
            between the Registrant and Medtronic, Inc.


<PAGE>

+10.7(2)    System  Design and  Procurement  Agreement  dated as of December 16,
            1994 between the Registrant and Pharmacia Biotech, Inc.

10.8(2)     Lease dated March 10, 1994  between  the  Registrant  and  Laborer's
            Pension/Milford  Investment  Corporation  for space  located at 155.
            Fortune  Boulevard,  Milford,  Massachusetts,  including Note in the
            original principal amount of $750,000.

10.9(2)     Registration  Rights Agreement dated as of February 21, 1990 between
            the Registrant,  the Worcester  Foundation for Biomedical  Research,
            Inc. and Paul C. Zamecnik.

10.10(2)    Registration  Rights Agreement dated as of June 25, 1990 between the
            Registrant and Nigel L. Webb.

10.11(2)    Registration  Rights  Agreement  dated as of  February  6, 1992
            between the Registrant and E. Andrews Grinstead, III.

10.12(2)    Registration  Rights  Agreement dated as of February 6, 1992 between
            the Registrant and Anthony J. Payne.

++10.13(2)  1990 Stock Option Plan, as amended.

++10.14(2)  1995 Stock Option Plan.

++10.15(2)  1995 Director Stock Plan.

++10.16(2)  1995 Employee Stock Purchase Plan.

10.17(2)    Form of Warrant  originally issued to Pillar  Investment  Limited to
            purchase  shares of Common Stock issued as placement  commissions in
            connection with the sale of shares of Series F Convertible Preferred
            Stock  and  in  consideration  of  financial  advisory  service,  as
            amended.

10.18(2)    Warrant  issued to Pillar S.A. to purchase  100,000 shares of Common
            Stock dated as of March 1, 1994, as amended.

10.19(2)    Warrant  issued to Pillar S.A. to purchase  100,000 shares of Common
            Stock dated as of March 1, 1995.

10.20(2)    Form of Warrant  issued to Pillar  Investment  Limited  to  purchase
            shares of Common Stock issued as placement commissions in connection
            with the sale of Units pursuant to the Series G Agreement.

++10.21(5)  Employment   Agreement  dated  as  of  March  1,  1997  between  the
            Registrant and E. Andrews Grinstead, III.

10.22(2)    Indemnification  Agreement  dated as of February 6, 1992 between the
            Registrant and E. Andrews Grinstead, III.


<PAGE>

++10.23(6)  Employment  Agreement dated March 1, 1997 between the Registrant and
            Dr. Sudhir Agrawal.

++10.24(2)  Consulting  Agreement  dated as of  February  21,  1990  between the
            Registrant and Dr. Paul C. Zamecnik.

10.25(2)    Master  Lease  Agreement  dated  as of  March 1,  1994  between  the
            Registrant and General Electric Capital Corporation.

+10.26(6)   Research,  Development and License Agreement dated as of January 24,
            1996 between the Registrant and G.D. Searle & Co.

+10.27(6)   Manufacturing  and Supply  Agreement  dated as of January  24,  1996
            between the Registrant and G.D. Searle & Co.

10.28(6)    Registration  Rights  Agreement dated as of January 24, 1996 between
            the Registrant and G.D. Searle & Co.

10.29(5)    Loan and  Security  Agreement  dated as of December 31, 1996 between
            the Registrant and Silicon Valley Bank.

10.30(7)    First Amendment to Loan and Security  Agreement dated March 30, 1998
            between Hybridon, Inc. and Silicon Valley Bank.

10.31(8)    Second Amendment to Loan and Security  Agreement dated May 19, 1998,
            effective as of April 30, 1998,  between Hybridon,  Inc. and Silicon
            Valley Bank.

10.32(9)    Third  Amendment to Loan and Security  Agreement dated September 18,
            1998 between Hybridon, Inc. and Silicon Valley Bank.

10.33(9)    Fourth  Amendment to Loan and Security  Agreement  dated October 30,
            1998, effective as of September 29, 1998 between Hybridon,  Inc. and
            Silicon Valley Bank.

10.34       Fifth  Amendment to Loan and Security  Agreement  dated  December 4,
            1998 between Hybridon, Inc. and Silicon Valley Bank.

10.35(5)    Warrant issued to Silicon  Valley Bank to purchase  65,000 shares of
            Common Stock dated as of December 31, 1996.

10.36(5)    Registration  Rights Agreement dated as of December 31, 1996 between
            the Registrant and Silicon Valley Bank.

+10.37(5)   Supply and Sales Agreement dated as of September 1, 1996 between the
            Registrant and P.E. Applied Biosystems.

10.38(2)    Registration  Rights  Agreement  dated as of March 26, 1997  between
            Forum Capital Markets LLC and the Registrant.


<PAGE>

10.39(2)    Warrant  Agreement  dated as of March 26, 1997 between Forum Capital
            Markets LLC and the Registrant.

+10.40(6)   Amendment No. 1 to License Agreement, dated as February 21, 1990 and
            restated as of  September  8, 1993,  by and  between  the  Worcester
            Foundation for Biomedical Research,  Inc. and the Registrant,  dated
            as of November 26, 1996.

10.41(10)   Letter  Agreement  dated May 12,  1997  between the  Registrant  and
            Pillar S.A.  amending the Consulting  Agreement dated as of March 1,
            1994 between the Registrant and Pillar S.A.

10.42(10)   Amendment dated July 15, 1997 to the Series G Convertible  Preferred
            Stock and Warrant  Purchase  Agreement dated as of September 9, 1994
            among the Registrant and certain purchasers, as amended.

10.43(1)    Consent Agreement dated January 15, 1998 between Silicon Valley Bank
            and the Registrant relating to the Silicon Agreement.

10.44(11)   Letter  Agreement  between the Registrant and Forum Capital  Markets
            LLC and Pecks Management  Partners Ltd. for the purchase of the Loan
            and Security Agreement with Silicon Valley Bank.

10.45(7)    Financial   Advisory   Agreement   between   Registrant  and  Pillar
            Investments Ltd. dated May 5, 1998.

10.46(7)    Placement Agency Agreement between Registrant and Pillar Investments
            Ltd. dated as of January 15, 1998.

+++10.47    Licensing  Agreement  dated March 12, 1999 by and between  Hybridon,
            Inc. and Integrated DNA Technologies, Inc.

21.1(2)     Subsidiaries of the Registrant.

23.1        Consent of Arthur Andersen LLP.

23.2        Consent of McDonnell Boehnen Hulbert & Berghoff.

27.1        Financial Data Schedule [EDGAR] - Year Ended December 31, 1998
- ------------------------------------------------

(1)         Incorporated  by  reference to Exhibits to the  Registrant's  Annual
            Report on Form 10-K for the year ended December 31, 1997.

(2)         Incorporated   by   reference   to  Exhibits  to  the   Registrant's
            Registration Statement on Form S-1 (File No. 33-99024).

(3)         Incorporated  by  reference to Exhibit  9(a)(1) to the  Registrant's
            Schedule 13E-4 dated February 6, 1998.


<PAGE>

(4)         Incorporated  by reference to Exhibits to the  Registrant's  Current
            Report on Form 8-K dated April 2, 1997.

(5)         Incorporated  by  reference to Exhibits to the  Registrant's  Annual
            Report on Form 10-K for the year ended December 31, 1996.

(6)         Incorporated  by  reference to Exhibits to the  Registrant's  Annual
            Report on Form 10-K for the year ended December 31, 1995.

(7)         Incorporated by reference to Exhibits to the Registrant's  Quarterly
            Report on Form 10-Q for the period ended March 31, 1998.

(8)         Incorporated by reference to Exhibits to the Registrant's  Quarterly
            Report on Form 10-Q for the period ended June 30, 1998.

(9)         Incorporated by reference to Exhibits to the Registrant's  Quarterly
            Report on Form 10-Q for the period ended September 30, 1998.

(10)        Incorporated by reference to Exhibits to the Registrant's  Quarterly
            Report on Form 10-Q for the period ended June 30, 1997.

(11)        Incorporated   by   reference   to  Exhibits  to  the   Registrant's
            Registration Statement on Form S-1 (File No. 333-69649).

+           Confidential  treatment  granted  as  to  certain  portions,   which
            portions are omitted and filed separately with the Commission.

++          Management contract or compensatory plan or arrangement  required to
            be filed as an  Exhibit  to the  Annual  Report on Form 10-K for the
            year ended December 31, 1997.

+++         Confidential  treatment  requested  as to  certain  portions,  which
            portions are omitted and filed separately with the Commission.





                                                                   Exhibit 10.34


                 FIFTH AMENDMENT TO LOAN AND SECURITY AGREEMENT


        This Fifth  Amendment is made,  effective as of the 4th day of December,
1998,  to that certain Loan and Security  Agreement  between  Hybridon,  Inc., a
Delaware  corporation  with  a  principal  place  of  business  at  155  Fortune
Boulevard, Milford, Massachusetts (the "Borrower"), and Silicon Valley Bank (the
"Bank")  dated as of  December  31,  1996,  as  amended.  The Loan and  Security
Agreement,  as  amended  to  date,  is  hereinafter  referred  to as  the  "Loan
Agreement." Capitalized terms used but not defined in this Fifth Amendment shall
have the meanings ascribed to them in the Loan Agreement,  or if not so defined,
shall have the meanings  ascribed to them in the Uniform  Commercial Code, or in
the case of  financial  and  accounting  terms,  in  accordance  with  generally
accepted accounting principles.

        Pursuant to the Loan Agreement and on the terms and conditions set forth
therein, on December 31, 1996, the Bank made a secured term loan to the Borrower
in the original  face amount of $7,500,000  (the "Loan").  On November 24, 1998,
Forum Capital Markets,  LLC ("Forum")  purchased the Bank's entire right,  title
and interest in and to the Loan,  including all  principal and unpaid  interest,
which at such time was in the  principal  amount of  $2,769,789.  Pursuant  to a
Purchase  and  Assignment  Agreement  dated  November  24, 1998  between  Forum,
Delaware State  Employees  Retirement Fund  ("Delaware  State"),  Declaration of
Trust for the Defined  Benefit  Plans of ICI  American  Holdings  Inc.  ("ICI"),
Declaration  of Trust for the  Defined  Benefit  Plans of Zeneca  Holdings  Inc.
("Zeneca"),  The J.W. McConnell Family Foundation ("McConnell"),  General Motors
Employees Domestic Group Trust ("GM"),  and Thermo Electron Balanced  Investment
Fund ("Thermo Electron") (Delaware State, ICI, Zeneca,  McConnell, GM and Thermo
Electron being hereinafter  referred to collectively as the "Pecks  Investors"),
Forum agreed to advance an additional $280,706 and the Pecks Investors agreed to
advance an  additional  $2,949,505 to the  Borrower,  and Forum  assigned to the
Pecks  Investors  a one-half  interest  in and to the Loan.  Forum and the Pecks
Investors are hereinafter  referred to together as the "Lenders." On December 1,
1998,  Forum advanced an additional  $280,706 to the Borrower and on December 4,
1998 the Pecks  Investors  advanced  the  following  additional  amounts  to the
Borrower:

               Delaware State               $1,838,249.32
               ICI                          $1,304,388.92
               Zeneca                       $1,203,810.80
               McConnell                    $1,134,497.42
               GM                           $1,134,551.01
               Thermo Electron              $1,133,907.53

Such  additional  amounts from Forum and the Pecks  Investors have increased the
aggregate outstanding principal amount of the Loan to $6,000,000.

        In consideration of the undertakings and obligations of the Borrower and
the Bank set forth  herein and for other good and  valuable  consideration,  the
receipt and sufficiency of which are hereby  acknowledged,  the Borrower and the
Lenders hereby agree as follows:


                                        1


<PAGE>

        1. The term  "Business  Day" shall be amended to refer to  Massachusetts
instead of California.

        2. The term "Maturity Date" shall be amended to mean November 30, 2003.

        3. Effective as of November 24, 1998, the term "Interest  Rate" shall be
amended to mean 8% per  annum,  which  shall be,  beginning  on such  date,  the
effective  interest rate on the  Borrower's  obligations in respect of the Loan,
notwithstanding  anything to the contrary in the Loan Agreement, as amended. The
Loan Agreement,  as amended, is hereby amended to delete any requirement therein
that the  Borrower  make any  additional  payments  to the Lender or the Bank in
excess of the interest and principal payments set forth in this Fifth Amendment.

        4. The amortization schedule of the Loan set forth in the Loan Agreement
shall be revised as follows:  no principal  shall be due until November 30, 2003
(unless the Obligations  shall become  immediately due and payable under Section
9.1 of the Loan Agreement).  Interest shall be payable monthly in arrears on the
last day of the month (or if such day is not a Business  Day, the next  Business
Day to occur).

        5. Section 6.9 of the Loan Agreement,  as amended,  is hereby amended to
read as follows:

               6.9   Minimum Liquidity.  Borrower shall maintain, as of the last
               calendar_day of each month,  Minimum Liquidity of Two Million and
               No/100 Dollars ($2,000,000.00). "Minimum Liquidity" is defined as
               consolidated  cash on hand  (other  than  cash in which an entity
               other  than  the  Lenders  or  their  assignees  has  a  security
               interest) (and cash  equivalents and marketable  securities) plus
               50% of accounts receivable.

        6. Section 10 of the First Amendment to the Loan and Security  Agreement
effective as of March 30, 1998, is hereby deleted.

        7. The Loan may not be prepaid,  in whole or in part,  at any time prior
to December 1, 2000, without the prior written consent of a majority in interest
of the Lenders.

        8. The principal  amount of the Loan, from time to time, and accrued but
unpaid interest thereon, shall be convertible,  in whole or in part, at Lender's
option,  into Common Stock of the  Borrower at a  conversion  price of $2.40 per
common share  (appropriately  adjusted for stock splits, stock dividends and the
like).

        9. All defaults and events of default which may exist on the date hereof
under the Loan Agreement are hereby waived.

        10. To the extent  possible,  this Fifth Amendment shall be construed to
be consistent with the provisions of the Loan Agreement;  however, to the extent
that  the  provisions  of  this  Fifth  Amendment  expressly  conflict  with  or
contradict  the provisions of the Loan  Agreement,  the provisions of this Fifth
Amendment shall be deemed to control.


                                        2


<PAGE>

        11. This Fifth  Amendment  represents the entire  agreement  between the
parties  with  respect  to the  modifications  contained  herein,  and  shall be
construed in accordance with the laws of the Commonwealth of Massachusetts as an
agreement  under seal.  The  Borrower  has  voluntarily  entered into this Fifth
Amendment  without  coercion  or  duress of any kind and has been or has had the
opportunity to have been represented by legal counsel of their choosing.

        WITNESS OUR hands and seals on this 4th day of December, 1998.

HYBRIDON, INC.                              FORUM CAPITAL MARKETS, LLC


By:  /s/ E. Andrews Grinstead, III          By:  /s/ C. Keith Hartley
     -----------------------------               --------------------


                                            DELAWARE STATE EMPLOYEES
                                                 RETIREMENT FUND
                                            DECLARATION OF TRUST FOR THE
                                                 DEFINED BENEFIT PLANS OF ICI
                                                 AMERICAN HOLDING INC.
                                            DECLARATION OF TRUST FOR THE
                                                 DEFINED BENEFIT PLANS OF
                                                 ZENECA HOLDINGS INC.
                                            THE J.W. McCONNELL FAMILY
                                                 FOUNDATION
                                            GENERAL MOTORS EMPLOYEES
                                                 DOMESTIC GROUP TRUST
                                            THERMO ELECTRON BALANCED
                                                 INVESTMENT FUND

                                            By:  PECKS MANAGEMENT PARTNERS LTD.

                                            By: /s/ Arthur W. Berry
                                                -------------------

                                        3



                                                                   Exhibit 10.47

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.

                               Licensing Agreement

This  Agreement is made  effective  this 12th day of March 1999,  by and between
Integrated DNA  Technologies,  Inc., a corporation  organized and existing under
the laws of Iowa  having  offices  at 1710  Commercial  Park,  Coralville,  Iowa
(hereinafter  called "IDT"), and Hybridon,  Inc., a Delaware  corporation having
its principal place of business at 155 Fortune Boulevard, Milford, Massachusetts
01757 (hereinafter called "Hybridon").

WHEREAS, IDT owns or controls certain technology,  proprietary information,  and
inventions hereinunder described as IDT Antisense Technology,  and is willing to
grant a * * * License to Hybridon under the rights contained therein,  according
to the terms hereunder described; and

WHEREAS, Hybridon owns or controls certain technology,  proprietary information,
and inventions  hereinunder described as Hybridon Antisense  Technology,  and is
willing to grant a * * * License to IDT under  those  rights,  according  to the
terms hereunder described;

NOW,  THEREFORE,  in  consideration  of the mutual  covenants and agreements set
forth below, the parties covenant and agree as follows:

Section 1.  Definitions.

        For the  purpose of this  Agreement,  the  following  definitions  shall
apply.

        A.  "Affiliates" shall mean any corporation, company, partnership, joint
            venture or other  entity,  which  controls,  is  controlled or under
            common  control with Hybridon or IDT as the case may be, and, in the
            case of  Hybridon,  provided  such  entities  agree in writing to be
            bound by the terms and provisions of this Agreement, shall also mean
            and include MethylGene Inc., and OriGenix  Technologies Inc. For the
            purposes  of this  definition,  control  shall  mean the  direct  or
            indirect  ownership of at least fifty percent (50%) or, if less than
            fifty percent (50%), the maximum percentage as allowed by applicable
            law of (a) the stock  shares  entitled  to vote for the  election of
            directors; or (b) ownership interest.

        B.  "Chimeric Antisense Technology" shall mean any oligonucleotide,  the
            nucleotide   sequence  of  which  has  complementarity  for  and  is
            hybridizable to a nucleotide  sequence within RNA transcribed from a
            targeted gene, which  oligonucleotide  meets at least one of the two
            sets of criteria described in Appendix B attached hereto.

        C.  "Confidential  Information"  shall mean this Agreement,  and any and
            all books,  records,  opinions of counsel and  business  information
            required  to be  supplied  to either  Party  under the terms of this
            Agreement.


                                      - 1 -


<PAGE>

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.

        D.  "Hybridon  Antisense  Technology"  shall  mean all  Hybridon  issued
            patents, Hybridon filed patents applications, or patents acquired by
            Hybridon  as of or  prior  to  the  date  of  the  signing  of  this
            agreement, to the extent that the claims of such patents and patents
            issuing   from  such   applications   fall   within   the  scope  of
            oligonucleotides defined herein as Chimeric Antisense Technology.

        E.  "Hybridon Licensed Product" shall mean and include any material that
            either (a) is covered by a claim of any patent within the definition
            of Hybridon  Antisense  Technology;  or (b) the manufacture,  use or
            sale of which would constitute, but for the license granted pursuant
            to this  Agreement,  an  infringement  of any Valid Claim within the
            definition of Hybridon Antisense Technology.

        F.  "Hybridon  Sublicensed  Product" shall mean any IDT Licensed Product
            discovered  and/or  developed in whole or in part by Hybridon or its
            Affiliates,  which is sublicensed to a third party for  manufacture,
            development, distribution and/or commercialization.

        G.  "IDT Antisense  Technology" shall mean Chimeric Antisense Technology
            covered  by  one  or  more  Valid  Claims  of * * * * * *;  and  all
            divisional, reissues, and foreign counterparts claiming and entitled
            to the right of priority from these patents and patent applications.

        H.  "IDT Licensed Product" shall mean and include any material or method
            that either (a) is covered by a Valid Claim of any patent within the
            definition of IDT Antisense Technology; or (b) the manufacture,  use
            or sale of  which  would  constitute,  but for the  license  granted
            pursuant  to this  Agreement,  an  infringement  of any Valid  Claim
            within the definition of IDT Antisense Technology.

        I.  "Interference  Settlement Agreement" shall mean the Agreement signed
            by the parties to United States  Interference No. 104,041,  attached
            hereto as Attachment 1.

        J.  "License"  shall  mean  the  License  granted  to  Hybridon  and its
            Affiliates  for IDT Antisense  Technology  for Medical  Applications
            and/or the License  granted to IDT and its  Affiliates  for Hybridon
            Antisense Technology for Research Applications, as the case may be.

        K.  "Licensed Products" shall mean IDT Licensed Products and/or Hybridon
            Licensed Products, as the case may be.


                                      - 2 -


<PAGE>

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.


        L.  "Licensee" shall mean IDT and its Affiliates and/or Hybridon and its
            Affiliates, as the case may be.

        M.  "Licensor" shall mean IDT and its Affiliates and/or Hybridon and its
            Affiliates, as the case may be.

        N.  "Medical  Applications"  shall mean * * * * * * *, including without
            limitation, * * * * * * * * *.

        O.  "Net Sales"  shall mean the * * * * , from sales of * * * * * *: (i)
            import,  export,  excise, good and services,  sales or similar taxes
            and custom duties;  (ii) reasonable listed trade discounts,  rebates
            and   allowances,   as  well   as  all   returns;   (iii)   packing,
            transportation,   shipping,  insurance  and  other  similar  charges
            incurred in connection  with and  necessary  for  completion of such
            dispositions;  (iv)  *  *  *  *  * *  *;  and  (v)  *  * * * * *  *.
            Notwithstanding  the  foregoing,  * * * * * * * * *. For purposes of
            this Agreement,  a distributor will not * * * * * and sales by * * *
            * * * *.

        P.  "Research Applications" shall mean all * * * * * * including but not
            limited to * * * * * * *, with the exception of * * * * * * *.

        Q.  " Valid Claim"  shall mean a claim of an issued  patent that has not
            been  ruled  invalid  or  unenforceable  by  a  court  of  competent
            jurisdiction in an unappealed or unappealable decision.

Section 2.  Grants of Licenses

        A.  IDT License to Hybridon.

            IDT grants to Hybridon  and its  Affiliates,  a * * * * * License to
            make, use, offer to sell, import, and sell IDT Licensed Products for
            all Medical  Applications.  The License  granted to Hybridon and its
            Affiliates  shall  be  * *  *  **  *  according  to  the  terms  and
            restrictions as established in subsection 2C herein.

            (i) * * * * *. IDT shall * * * * *, including, but not limited to, *
                * * * *.

            (ii)* * * * *. IDT shall not * * * * *, with such licenses  having *
                * * * * than  those  established  herein,  unless * * * * *. IDT
                hereby * * * * * to make * * * * * to * * * * *, for any reason,
                including  but not  limited to: (1) * * * * *; (2) the * ** * *;
                and (3) any * * * * *. Under no circumstances shall* * * * * .


                                      - 3 -


<PAGE>

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.


       B.     Hybridon License to IDT.

              Hybridon  grants to IDT and its  Affiliates  * * * * * license  to
              use, manufacture, offer to sell, import and sell Hybridon Licensed
              Products for Research Applications.

              (i)    * * * * *. Hybridon shall * * * * *.

              (ii)   * * * * *. Hybridon shall not * * * * *, unless * * * * *.

              (iii)  License Clarified. Within sixty (60) days of the signing of
                     this  Agreement,  Hybridon  shall deliver to IDT a complete
                     list of  patents  and  patent  applications  owned by,  and
                     assigned or  exclusively  licensed to Hybridon  included in
                     the definition of Hybridon Antisense  Technology.  The list
                     shall be identified as Appendix A and will be  incorporated
                     into this Agreement upon acceptance by IDT.

       C.     Sublicenses.

              (i)    Upon grant of the license,  Hybridon and its Affiliates may
                     grant  written   sublicenses   to  third  parties  for  the
                     manufacture,     development,      distribution,     and/or
                     commercialization  of any IDT Licensed  Product  discovered
                     and/or  developed  in whole or in part by  Hybridon or such
                     Affiliates  (a Hybridon  Sublicensed  Product)  for Medical
                     Applications.  Hybridon  will inform IDT of the identity of
                     any  sublicensee  and the nature of such sublicense * * * *
                     *. Any agreement granting a sublicense shall state that the
                     sublicense  is  subject  to the  terms  of this  Agreement.
                     Hybridon  shall  have the  same  accounting  and  reporting
                     responsibilities for the activities of any sublicensee,  as
                     if the activities were directly those of Hybridon.

              (ii)   The Hybridon License to IDT and its Affiliates shall be * *
                     * * *.

Section 3.  Consideration.

       A.     Initial License Fee.

              Upon execution of this Agreement, Hybridon agrees to pay to* * * *
              * according to the following schedule:

              (i)    * * * * *;

              (ii)   * * * * *; and

              (iii)  * * * * *.


                                      - 4 -


<PAGE>

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.


       B.     * * * * *.

              (i)    * * * * *.  Hybridon  agrees  to  pay to * * * * * by or on
                     behalf  of  Hybridon,   its   Affiliates  or   sublicensees
                     hereunder, or its foreign equivalent.

                     Hybridon  shall  notify  *  * * *  *  ,  by  Hybridon,  its
                     Affiliates or sublicensees.

                     For  each * * * * *,  unless  compliance  with  the  notice
                     provisions of 3.B(iii) herein, allows for an extension.

              (ii)   * * * * *. Hybridon  agrees to pay to* * * * * or a foreign
                     equivalent.

                     For  each* * * * * ,  unless  compliance  with  the  notice
                     provisions of 3.B(iii) herein, allows for an extension.

                     Payment of the * * * * *, unless compliance with the notice
                     provisions of 3.B(iii) herein, allows for an extension.

              (iii)  Hybridon shall notify IDT * * * * *if Hybridon is unable to
                     * * * * * to IDT  for a * * * * * or an * * * * * sold by *
                     * * * * or * * * * *, within the time allotted in the above
                     numbered  sections  because  of * * * * * or * * * * * . In
                     such notification, Hybridon shall * * * * * . Hybridon will
                     make payment to IDT the* * * * * .

              Notwithstanding  the foregoing,  products developed  utilizing IDT
              Licensed Technology, but which products do not themselves infringe
              any Valid Claim, are* * * * *.

       C.     * * * * *

              (i)    In further  consideration  for the License  granted herein,
                     Hybridon agrees to pay to IDT the following* * * * * :

                     (1)    * * * * *,

                      * * * * *

                     (2)    * * * * *,

                      * * * * *

                      (3) * * * * * .


                                      - 5 -


<PAGE>

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.


              (ii)   IDT agrees to pay to Hybridon * * * * *.

                     Notwithstanding the foregoing, products developed utilizing
                     IDT or Hybridon Licensed Technology,  but which products do
                     not themselves infringe any Valid Claim, are * * * * *.

       D.     Accounting/Payments.

              (i)    For each  fiscal  year in which  there  are Net  Sales of a
                     Licensed Product, each Licensee shall prepare, or cause its
                     Affiliates or sublicensees  to prepare,  deliver and pay to
                     Licensor a  quarterly  estimate of the * * * * * due to the
                     Licensor under Section 3.D,* * * * *.

              (ii)   * * * * * *,  Licensee  shall prepare and deliver an annual
                     statement  of the total * * * * * due to  Licensor  for the
                     fiscal year  expired  under  Section  3.D.  Licensee  shall
                     tender payment of the balance owed for the year,  including
                     all  payments  owed  for the  fourth  quarter  of the  year
                     expired,  and any  necessary  adjustments  to the quarterly
                     estimate payments  previously paid. Each quarterly estimate
                     or annual  payment shall be  accompanied  by a report which
                     shall  indicate the  estimated or actual Net Sales,  as the
                     case may be, by Licensee for the previous  period and shall
                     show the amount of * * * * * due Licensor  with  sufficient
                     detail  to  enable  confirmation  of  the  calculations  by
                     Licensor.

              (iii)  Except as otherwise directed, all amounts owing to Licensor
                     under  this  Agreement  shall  be paid in U.S.  dollars  to
                     Licensor at the addresses  provided in Section 12(a). * * *
                     * * owing with  respect to Net Sales  stated in  currencies
                     other  than U.S.  dollars  shall be  converted  at the rate
                     shown in the  Federal  Reserve  Noon  Valuation  - Value of
                     Foreign Currencies on the day preceding the payment.

Section 4.  Recordkeeping.

       A.     Licensee,  its Affiliates and its sublicensee(s)  shall keep books
              and records  sufficient to verify the accuracy and completeness of
              Licensee's and its sublicensee(s)'s  accounting referred to above,
              including  without  limitation  sales,  accounts  receivable,  and
              invoice  records  relating  to IDT  Licensed  Products or Hybridon
              Licensed Products. Such books and records shall be preserved for a
              period not less than five years after they are created  during and
              after the term of this Agreement.


                                      - 6 -


<PAGE>

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.


       B.     Licensee,  its  Affiliates and its  sublicensee(s)  shall take all
              steps  necessary so that  Licensor  may,  within sixty days of its
              request,  review  and copy all the books and  records  at a single
              U.S.  location  to  verify  the  accuracy  of  Licensee's  and its
              sublicensee(s)'s  accounting.  Such review  shall be made not more
              than once each  fiscal  year,  upon  reasonable  notice and during
              regular  business hours, at the expense of Licensor by a certified
              public accountant to whom Licensee has no reasonable objection.

       C.     If a * * * * * * for a fiscal year is  determined,  Licensee,  its
              Affiliates or  sublicensee(s)  shall pay the * * * * * outstanding
              within thirty (30) days of receiving  written notice thereof,  and
              shall reimburse Licensor for the cost of the inspection.

Section 5.  Patent Prosecution and Maintenance Publications.

       A.     Prosecution and Maintenance.

              The  preparation,  filing,  prosecution,  and  maintenance  of all
              patents and patent  applications -- domestic,  international,  and
              foreign -- included in the definition of IDT Antisense Technology,
              shall remain the exclusive  responsibility of IDT. IDT retains the
              exclusive   right  and   authority  to  make  all   decisions  and
              determinations  regarding the prosecution and maintenance of those
              patents  and  patent   applications.   The  preparation,   filing,
              prosecution,   and   maintenance   of  all   patents   and  patent
              applications -- domestic, international and foreign -- included in
              the definition of Hybridon Antisense Technology,  shall remain the
              exclusive   responsibility  of  Hybridon.   Hybridon  retains  the
              exclusive   right  and   authority  to  make  all   decisions  and
              determinations  regarding the prosecution and maintenance of those
              patents and patent applications.

       B.     Patent Marking.

              Hybridon and IDT shall comply with all  applicable  United  States
              and foreign  jurisdiction  laws in respect of patent  marking,  if
              any.

       C.     Ownership.

              (i)    Acknowledgments.   All  patent   rights   and   proprietary
                     information  included  in IDT  Antisense  Technology  shall
                     remain the sole  property  of IDT.  All  patent  rights and
                     proprietary  information  included  in  Hybridon  Antisense
                     Technology shall remain the sole property of Hybridon.


                                      - 7 -


<PAGE>

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.


       D.     Infringement by Third Parties.

              In the event that either party believes there is  infringement  in
              that  party's  field  of use of any  patent  included  within  IDT
              Antisense  Technology or Hybridon Antisense  Technology under this
              Agreement,  that party  shall  provide the other party with prompt
              written notification  thereof.  During the term of this Agreement,
              the  Licensor of the patent  being  infringed  shall have the sole
              right, but not the obligation,  to bring and control any action or
              proceeding  at its own  expense  and by  counsel of its own choice
              against any such infringement. If the Licensor of the patent being
              infringed elects to prosecute such infringement, the total cost of
              any  infringement  action  shall be borne by the  Licensor and the
              Licensor shall keep any recovery or damages for past  infringement
              derived therefrom.

       E.     Infringement of Third Party Rights.

              (i)    In the  event  that  either  party  receives  notice  of or
                     believes there is infringement by Licensee,  or if there is
                     asserted  infringement  by  Licensee  of any third  party's
                     intellectual property  (collectively,  "Alleged Third Party
                     Rights") by reason of the manufacture, import, use, sale or
                     offer for sale of any product  arising out of IDT Antisense
                     Technology  or  Hybridon  Antisense  Technology,  the party
                     having knowledge of the alleged  infringement shall provide
                     the other party with prompt written  notification  thereof.
                     Licensee shall have the right to control any defense of any
                     claim of  infringement of Alleged Third Party Rights at its
                     own expense and any counsel of its choice.

              (ii)   In the event that  Licensee  incurs  any  costs,  attorneys
                     fees,  damage  awards,  or other  penalties  relating to an
                     alleged  or  proven  act of  infringement,  Licensee  shall
                     indemnify  and  hold  harmless  Licensor,  and  either  the
                     University of Iowa Research  Foundation/University of Iowa,
                     or the University of Massachusetts  Medical Center,  as the
                     case may be, for all such costs and expenses.

Section 6.  Limitation of Liability, Indemnification, Negation of Warranties.

       A.     Limitation of Liability.

              IDT shall not be liable to Hybridon, its Affiliates, sublicensees,
              successors,  or assigns for any loss of profits, loss of business,
              interruption   of   business,   nor  for   indirect,   special  or
              consequential  damages of any kind under this Agreement.  Hybridon
              shall  not  be  liable  to  IDT,  its  Affiliates,   sublicensees,
              successors,  or assigns for any loss of profits, loss of business,
              interruption   of   business,   nor  for   indirect,   special  or
              consequential damages of any kind under this Agreement.


                                      - 8 -


<PAGE>

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.


       B.     Patent Rights.

              The  parties  warrant  that  except as  otherwise  provided  under
              Section  10 of this  Agreement  with  respect  to U.S.  Government
              interests, each has the right to grant the Licenses granted to the
              other party in this  Agreement.  IDT warrants that it does not own
              or control  any  patents  or patent  applications  with  claims to
              antisense  compounds  and/or methods not already  disclosed in the
              definition of "IDT Antisense Technology."

       C.     No Warranties.

              Except as expressly  set forth  herein,  IDT and Hybridon  make no
              representations,  extend no warranties of any kind, either express
              or implied, and assume no responsibilities whatsoever with respect
              to use,  sale,  or  other  disposition  by  Hybridon,  IDT,  their
              Affiliates, sublicensees or their vendees or other transferees, of
              IDT Licensed Products or Hybridon Licensed Products, respectively.

              Except as expressly set forth herein,  nothing in this  Agreement,
              nor any prior communication, shall be construed as:

              (i)    a warranty or  representation  by IDT or Hybridon as to the
                     validity  or scope of any of the patents  contained  within
                     IDT Antisense Technology or Hybridon Antisense Technology;

              (ii)   a warranty or representation that anything made, used, sold
                     or otherwise disposed of under the Licenses granted in this
                     Agreement  will or  will  not  infringe  patents  of  third
                     parties; or

              (iii)  an  obligation  to furnish any know-how not provided in IDT
                     Antisense  Technology or Hybridon  Antisense  Technology or
                     any services other than those specified in this Agreement.

       D.     Indemnification.

              Hybridon  and IDT  shall  at all  times  during  the  term of this
              Agreement and thereafter,  indemnify,  defend and hold each other,
              the University of Iowa Research Foundation/University of Iowa, the
              University  of  Massachusetts  Medical  Center and the authors and
              inventors  of IDT  Antisense  Technology  and  Hybridon  Antisense
              Technology,  harmless  against all claims and expenses,  including
              legal expenses and reasonable  attorneys fees,  arising out of the
              death of or injury to any  person or  persons or out of any damage
              to  property  and  against any other  claim,  proceeding,  demand,
              expense and liability of any kind whatsoever resulting


                                      - 9 -


<PAGE>

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.


              from the production, manufacture, sale, use, lease, consumption or
              advertisement  of products or processes  arising from any right or
              obligation of IDT or Hybridon or any of its sublicensee(s) granted
              herein. Notwithstanding the above, each party at all times reserve
              the  right  to  retain  counsel  of its  own  to  defend  its  own
              interests.

       E.     Insurance.

              IDT  and  Hybridon   warrant  that  each  will  use   commercially
              reasonable  efforts  to  maintain  liability   insurance  coverage
              appropriate  to the risk  involved  in the sale and  marketing  of
              Licensed  Products,  and shall include in the  calculation of said
              risk, each parties'  responsibility for indemnification in Section
              6D herein.  Notwithstanding the above, failure to obtain liability
              insurance  for the sale of  research  products  by IDT or Hybridon
              shall not be a breach of this clause.

Section 7.  Confidential Information.

The following  provisions  relate to  restrictions  on the disclosure and use of
Confidential Information by the parties:

       A.     Confidentiality.   Hybridon  and  IDT  each  agrees  to  treat  as
              confidential  and to use only in the conduct of its business,  all
              Confidential Information disclosed to it by the other party.

       B.     Non-Disclosure  and  Non-Use.  Hybridon and IDT each agrees not to
              disclose any of the  Confidential  Information  received  from the
              other party to any unauthorized  third party and not to use any of
              the  Confidential  Information  except to fulfill the terms of the
              Agreement,  for a period of five (5) years from the receipt of the
              Confidential Information.

       C.     Release from Restrictions.  All information which is characterized
              as Confidential Information shall cease to be confidential and the
              receiving party shall be released from its respective  obligations
              under Sections 7A and 7B hereof if such information (a) is legally
              known to or was in the  possession of the  receiving  party at the
              time of the  disclosure;  (b) legally is or has become part of the
              public domain  through no act or omission of the receiving  party;
              (c) has been  disclosed to the  recipient by a third party without
              restriction as to the use or disclosure of the information; (d) is
              available  to the general  public as a result of a  governmentally
              required release or disclosure; or (e) is required to be disclosed
              by  the  laws,   regulations  or  otherwise  of  any  governmental
              authority,   including  without  limitation,  the  Securities  and
              Exchange  Commission and the U.S. Food and Drug  Administration as
              determined by counsel of the receiving or disclosing party.


                                     - 10 -


<PAGE>

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.


Section 8.  Term and Termination.

       A.     The word  "termination"  and  cognate  words  such as  "term"  and
              "terminate",  as used in this  Section 8,  whether  applied to the
              Agreement or an individual  License,  are to be read, except where
              the contrary is  specifically  indicated,  as omitting  from their
              effect the following  rights and  obligations,  all of which shall
              survive any  termination  to the degree  necessary to permit their
              complete fulfillment or discharge:

              (i)    Licensor's  right to  receive  or  recover  and  Licensee's
                     obligation  to pay * * * * * *  accrued  or  accruable  for
                     payment at the time of any termination.

              (ii)   Licensee's  obligation to maintain  records and  Licensor's
                     right to receive final year accounting  reports as provided
                     in Section 3.E.

              (iii)  Any  cause of action or claim of  Licensor,  accrued  or to
                     accrue because of any breach or default by the Licensee;

              (iv)   The  rights  and  obligations  of  both  parties  regarding
                     confidentiality as defined in Section 7 herein;

              (v)    The warranty,  indemnification and insurance  provisions as
                     set forth in Sections 6.C, 6.D and 6.E.

       B.     The term of this  Agreement  shall extend until the last patent to
              expire  included  within  IDT  Antisense  Technology  or  Hybridon
              Antisense Technology, whichever expires later.

       C.     In the event either party;

              (i)    shall  materially  breach any of the terms,  conditions and
                     agreements  contained in this Agreement,  including but not
                     limited  to failure to pay or make  corrected  payments  of
                     Royalties in a timely fashion; or

              (ii)   assigns or attempts to assign this  Agreement,  the License
                     or any interest herein or therein without the prior written
                     consent of the other party or except as otherwise permitted
                     in Section 9;

                     then the alleging  party may, at its  election,  notify the
                     other party of the alleged breach giving the other party 30
                     days' written notice to cure the breach or begin good faith
                     negotiations to resolve such alleged breach. If the alleged
                     breach is not resolved to the  satisfaction of the alleging
                     party  within  60 days of the first  giving  of notice  the
                     alleging party may,


                                     - 11 -


<PAGE>

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.

                     at its option, bring arbitration  proceedings under Section
                     11.D. In the event of a good faith  dispute about  monetary
                     obligations,  the  notified  party will pay any  undisputed
                     amounts to the alleging party and pay any disputed  amounts
                     into  escrow  pending  resolution  of  such  dispute,  with
                     payment to be made to the prevailing  party.  The * * * * *
                     licenses granted hereunder are not terminable except in the
                     event of bankruptcy of a Licensee and the continuing rights
                     of sublicensees and others under this Section 8.

       D.     IDT's Rights Should Hybridon Become Bankrupt.

              IDT shall have the right to  terminate  Hybridon's  License to IDT
              Antisense  Technology granted pursuant to this Agreement under the
              following circumstances:  (i) the admission by Hybridon in writing
              of its insolvency or bankruptcy, (ii) the making by Hybridon of an
              assignment  of  substantially  all its assets  for the  benefit of
              creditors, (iii) an application by Hybridon for the appointment of
              a trustee or receiver  for  Hybridon,  (iv) the  appointment  of a
              trustee  or  receiver  for  Hybridon,  (v) the  institution  by or
              against Hybridon of any bankruptcy,  reorganization,  arrangement,
              insolvency or  liquidation  proceedings or other  proceedings  for
              relief under any  bankruptcy  law or similar law for the relief of
              debtors which is allowed against  Hybridon,  or is consented to or
              is not dismissed,  stayed or otherwise nullified within sixty (60)
              days after the  institution  thereof,  or (vi) Hybridon  ceases to
              carry  on  business  as  a  going  concern.   Notwithstanding  the
              foregoing,   Hybridon  shall  have  the  right  to  grant  to  its
              sublicensee(s)   the  power  to  assume   Hybridon's   rights  and
              obligations  under its License  and its  Affiliates  shall  retain
              their  rights and  obligations  under this  Agreement,  limited to
              Hybridon  Sublicensed  Products.  Hybridon,  and its  successor in
              interest,  however  organized,  shall, to the extent  permitted by
              law,  maintain  in  full  IDT's  License  to  Hybridon   Antisense
              Technology  granted  pursuant  to  this  Agreement.  In  addition,
              subject to the foregoing,  if University of Massachusetts  Medical
              Center  ("UMMC")  terminates its license with Hybridon for certain
              Hybridon  Antisense  Technology  as a result of any of the  events
              listed in the first  sentence of this  paragraph,  UMMC shall have
              the right  for a period  of 180 days  after  said  termination  to
              assume the rights and obligations of Hybridon hereunder and within
              the first 180 days  thereafter  shall  have the right to assign or
              sublicense all rights and obligations of Hybridon hereunder to one
              and only one party (a "Subsequent Licensee") to whom UMMC regrants
              a  license  under  such  formerly  licensed   Hybridon   Antisense
              Technology. Such Subsequent Licensee shall have the same rights to
              sublicense  hereunder as Hybridon had prior to the  termination of
              its license hereunder.


                                     - 12 -


<PAGE>

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.

       E.     In the event IDT:

              (i)    shall  become   insolvent,   bankrupt  or  subject  to  the
                     provisions  of the  United  States  Bankruptcy  Code or any
                     other similar legislation of any jurisdiction, or makes any
                     assignment for the benefit of creditors, fails to generally
                     to pay its debts as they become due, is adjudged  bankrupt,
                     or otherwise acknowledges its insolvency,  or if a receiver
                     custodian  or trustee of IDT's  property or a major part of
                     IDT's property is appointed, or if any other proceeding for
                     relief  under any  bankruptcy  law or  similar  law for the
                     relief of debtors is instituted by or against IDT; or

              (ii)   ceases to carry on business as a going concern;

                     then  Hybridon  shall  have the  right to  terminate  IDT's
                     License to Hybridon  Antisense  Technology granted pursuant
                     to this  Agreement.  IDT,  and its  successor  in interest,
                     however organized,  shall maintain, to the extent permitted
                     by law,  the IDT  License to Hybridon  granted  pursuant to
                     this Agreement.

       F.     Waiver of Terms.  No waiver of any breach of any term or provision
              of this  Agreement  shall be effective  or binding  unless made in
              writing and signed by the party purporting to give the waiver.  No
              condoning,  excusing or waiver by any party of any default, breach
              or  non-observance  by the  other  party  at any  time or times in
              respect of any  covenant,  proviso or condition  contained  herein
              shall  operate  as  waiver of that  party's  rights  hereunder  in
              respect  of  any  continuing  or  subsequent  default,  breach  or
              non-observance, and no waiver shall be inferred from or implied by
              anything  done or  committed  to be done by the party having those
              rights.

       G.     Rights and Obligations after Termination.  Upon the termination of
              a  License  resulting  from  the  provisions  of 8.C,  8.D and 8.E
              herein,  the Licensee and its  sublicensee(s),  if any, shall have
              the  right,   within  six  (6)  months   following  such  date  of
              termination,  to sell or dispose of Licensed Products completed or
              substantially completed on the date of termination and to complete
              orders,  outstanding on such date of termination for such products
              pursuant to the terms of this Agreement.

       H.     Successors  in  Interest.  Should  IDT and/or  Hybridon,  or their
              assigns become insolvent, bankrupt or subject to the provisions of
              the United States Bankruptcy Code or any other similar legislation
              of any jurisdiction, the rights of the University of Iowa Research
              Foundation  and the  University of  Massachusetts  Medical  Center
              pertaining  to  retention,  reversion,  and/or  assumption  of the
              insolvent  parties interest in the patents  described herein shall
              not be  abrogated  in any  way by any  term or  provision  of this
              Agreement.


                                     - 13 -


<PAGE>

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.


Section 9.  Assignability.

       This Agreement may not be transferred or assigned by either party without
       the prior  written  consent of the other party,  except that Licensee may
       freely assign this Agreement to (i) an Affiliate,  if Licensee guarantees
       the full performance of its Affiliates' obligations hereunder, or (ii) an
       entity acquiring  substantially  all of Licensee's  business to which the
       License  relates.  Any  purported  assignment  in  contravention  of this
       section shall, at the option of the non-assigning party, be null and void
       and of no effect.

Section 10.  United States Government Interests.

       It is understood that if the United States Government (through any of its
       agencies or otherwise) has funded research, during the course of or under
       which any of the  inventions  of the patents  contained in a License were
       conceived or made, the United States Government is entitled,  as a right,
       under the provisions of 35 U.S.C. ss. 200-212 and applicable  regulations
       of  Chapter  37 of the Code of Federal  Regulations,  to a  nonexclusive,
       nontransferable,   irrevocable   paid-up  license  to  practice  or  have
       practiced  the  invention  of such patent for  government  purposes.  Any
       license  granted to Licensee in this  Agreement  shall be subject to such
       right.

Section 11.  Miscellaneous.

       A.     Applicable  Law. This  Agreement  shall be construed in accordance
              with the internal laws of the State of Illinois. If any provisions
              of this Agreement are or shall come into conflict with the laws or
              regulations of any jurisdiction or any governmental  entity having
              jurisdiction over the parties or this Agreement,  those provisions
              shall be deemed automatically deleted, if such deletion is allowed
              by relevant  law, and the remaining  terms and  conditions of this
              Agreement  shall  remain  in  full  force  and  effect.  If such a
              deletion  is not so  allowed or if such a  deletion  leaves  terms
              thereby made clearly  illogical or  inappropriate  in effect,  the
              parties agree to substitute  new terms as similar in effect to the
              present  terms  of this  Agreement  as may be  allowed  under  the
              applicable   laws  and   regulations.   The  parties   hereto  are
              independent contractors and not joint ventures or partners.

       B.     Construction/Effect.  The parties  acknowledge that this Agreement
              has been the  subject  of full  opportunity  for  negotiation  and
              amendment  and that the party  who has  taken the role of  drafter
              shall not suffer any adverse construction of any terms or language
              of this Agreement because of such role.

       C.     Force Majeure.  A party hereto shall not be deemed in default with
              respect  to the  performance  of or  compliance  with  the  terms,
              covenants,  agreements conditions or provisos of this Agreement if
              the failure to perform or comply


                                     - 14 -


<PAGE>

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.

              shall be due to any event of force majeure.  "Force majeure" shall
              include  natural  disasters,  acts of God,  or any other  event or
              cause beyond the control of the party claiming the benefit of this
              paragraph and which that party could not reasonably have protected
              itself  against,  provided  however  that  lack of funds or credit
              shall not constitute an event of force majeure.

       D.     Disputes-- Arbitration. The parties agree to attempt initially, to
              solve all claims,  disputes,  or controversies  arising under, out
              of, or in connection  with this Agreement by conducting good faith
              negotiations.  Except with  respect to disputes as to the validity
              of patents, applications for injunctions, specific performance, or
              other  equitable  relief,   any  dispute  arising  out  of  or  in
              connection   with  this   Agreement  or  any  legal   relationship
              associated  therewith,  that  cannot be  resolved  amicably by the
              parties, shall be finally resolved by arbitration. The arbitration
              shall be conducted in accordance with the arbitration rules of the
              American Arbitration  Association ("AAA") then in force, by one or
              more   arbitrators   appointed  in  accordance  with  said  rules;
              provided,   however,  that  arbitration  proceedings  may  not  be
              instituted  until the party  alleging  breach of this Agreement by
              the other party has given the other party not less than sixty (60)
              days' notice to remedy any alleged  breach and the other party has
              failed  to do so.  The  place of  arbitration  shall  be  Chicago,
              Illinois.  The award rendered shall be final and binding upon both
              parties.   The   judgement   rendered   shall   include  costs  of
              arbitration,  reasonable  attorney's fees and reasonable costs for
              any expert and other  witnesses.  The  arbitration  may  expressly
              consider the amounts paid  pursuant to Sections  3.B, 3.C and 3.D,
              in considering any claims of any damages.  Judgment upon the award
              may be entered in any court having  jurisdiction,  or  application
              may be made to such  court for  judicial  acceptance  of the award
              and/or an order of  enforcement.  Disputes  as to the  validity of
              patents   shall  be   resolved   by  the  courts  of   appropriate
              jurisdiction.

Section 12.  Notices.

       Any  notice  required  to be given  pursuant  to the  provisions  of this
       Agreement  shall be in writing  and shall be deemed to have been given at
       the earlier of the time when actually  received as a  consequence  of any
       effective method of delivery, including but not limited to hand delivery,
       transmission by telefax, or delivery by a professional courier service or
       the time when sent by  certified  or  registered  mail  addressed  to the
       party.  Any  notice of change of  address  shall be  effective  only upon
       actual receipt,  by the persons listed below or other formally authorized
       person(s) acting in their behalf.


                                     - 15 -


<PAGE>

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.


               (a)    Joseph A. Walder, M.D., Ph.D.
                      Integrated DNA Technologies, Inc.
                      President & CEO
                      1710 Commercial Park
                      Coralville, IA  52241-9802

               (b)    Cheryl M. Northrup, J.D.
                      Hybridon, Inc.
                      Vice President and General Counsel
                      155 Fortune Blvd
                      Milford, MA  01757

Section 13.  Integration.

       This agreement  constitutes  the full  understanding  between the parties
       with  reference  to the  subject  matter  hereof,  and no  statements  or
       agreements by or between the parties,  whether orally or in writing, made
       prior to or at the signing hereof, shall vary or modify the written terms
       of this Agreement. Neither party shall claim any amendment, modification,
       or release from any  provisions  of this  Agreement by mutual  agreement,
       acknowledgement,  or  otherwise,  unless  such  mutual  agreement  is  in
       writing, signed by the other party, and specifically states that it is an
       amendment to this Agreement.

Section 14.  Benefits.

       All terms and  provisions of this  Agreement  shall bind and inure to the
       benefit of the parties hereto,  and upon their respective  successors and
       assigns as those are permitted under the terms of this Agreement.

Section 15.  Contract Formation and Authority.

       The  persons  signing on behalf of IDT and  Hybridon  hereby  warrant and
       represent that they have authority to execute this Agreement on behalf of
       the party for whom they have signed.


                                     - 16 -


<PAGE>

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.



IN WITNESS WHEREOF,  the parties hereto have duly executed this Agreement on the
dates indicated below.


INTEGRATED DNA TECHNOLOGIES, INC.   HYBRIDON, INC.

/s/ Joseph A. Walder, M.D., Ph.D.           /s/ E. Andrews Grinstead III
- ---------------------------------           ----------------------------
Joseph A. Walder, M.D., Ph.D.                   E. Andrews Grinstead III
President                                       President

Date: March 15, 1999                        Date:   March 12, 1999
      ------------------------------                ----------------------------


                                     - 17 -


<PAGE>

          Confidential materials omitted and filed separately with the
                       Securities and Exchange Commission.
                           Asterisks denote omissions.


                                   APPENDIX B
                          Chimeric Antisense Technology

"Chimeric Antisense  Technology" shall mean any oligonucleotide,  the nucleotide
sequence of which has  complementarity  for and is  hybridizable to a nucleotide
sequence  within RNA  transcribed  from a targeted gene,  which  oligonucleotide
meets at least one set of the following two sets of criteria:

Criteria Set (1)

(a)    * * * * *; and

(b)    * * * * * ; and

(c)    * * * * *.

or:

Criteria Set (2)

(i)    * * * * *; and

(ii)   * * * * *; and

(iii)  * * * * *.


                                     - 18 -





                                                                    Exhibit 23.1


                    CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS

As independent  public  accountants,  we hereby consent to the use of our report
dated  February 19, 1999 (except with respect to the matter  disclosed  in Note
7(b) as to which the date is April 15, 1999) included in this Form 10-K into the
Company's  previously filed Registration  Statement File No.'s 33-3898,  33-3900
and 33-3902.


                                                         /s/ Arthur Andersen LLP


Boston, Massachusetts
April 15, 1999


                                     - 19 -




                                                                    Exhibit 23.2



             [Letterhead of McDonnell, Boehnen, Hulbert & Berghoff]



                                                   April 14, 1999


Hybridon, Inc.
155 Fortune Boulevard
Milford, Massachusetts 01757

Dear Sirs:

        McDonnell,  Boehnen, Hulbert & Berghoff hereby consents to the reference
to our firm under the section "Business -- Patents,  Trade Secrets and Licenses"
in the Hybridon, Inc. Annual Report on Form 10-K for the year ended December 31,
1998.
                                            Very truly yours,

                                            /s/ John J. McDonnell
                                            ---------------------
                                            John J. McDonnell

JJM:de


                                     - 20 -


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