TRANSKARYOTIC THERAPIES INC
10-K, 1999-03-31
BIOLOGICAL PRODUCTS, (NO DIAGNOSTIC SUBSTANCES)
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                          SECURITIES AND EXCHANGE COMMISSION

                                WASHINGTON, D.C. 20549

                                      FORM 10-K

     FOR ANNUAL AND TRANSITION REPORTS PURSUANT TO SECTIONS 13 OR 15(d) OF THE
                          SECURITIES EXCHANGE ACT OF 1934

(MARK ONE)

        [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 NO. 0-21481

                            TRANSKARYOTIC THERAPIES, INC.
                (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

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


                DELAWARE                               04-3027191      
     (STATE OR OTHER JURISDICTION OF                (I.R.S. EMPLOYER   
     INCORPORATION OR ORGANIZATION)                IDENTIFICATION NO.) 
                                    


            195 ALBANY STREET
        CAMBRIDGE, MASSACHUSETTS                         02139    
         (ADDRESS OF PRINCIPAL                         (ZIP CODE) 
           EXECUTIVE OFFICES)   


          REGISTRANT'S TELEPHONE NUMBER, INCLUDING AREA CODE: (617) 349-0200

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

          SECURITIES REGISTERED PURSUANT TO SECTION 12(b) OF THE ACT:  NONE

             SECURITIES REGISTERED PURSUANT TO SECTION 12(g) OF THE ACT:
                             COMMON STOCK, $.01 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>

     As of March 5, 1999, the approximate aggregate market value of the voting
stock held by non-affiliates of the registrant was $214,000,000, based on the
last reported sale price of the registrant's Common Stock on the Nasdaq National
Market as of the close of business on March 5, 1999.  There were 19,166,209
shares of Common Stock outstanding as of March 5, 1999.



                        DOCUMENTS INCORPORATED BY REFERENCE

Document                                                    10-K Part
- --------                                                    ---------
Specifically Identified Portions of the Registrant's
Proxy Statement for the Annual Meeting of Stockholders
to be held on June 10, 1999                                    III

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

<PAGE>

PART I

ITEM 1.    BUSINESS

SUMMARY

     Transkaryotic Therapies, Inc. ("TKT" or "the Company") is a 
biopharmaceutical company dedicated to the development and commercialization 
of products based on its three proprietary development platforms--Gene 
Activated(TM) proteins, Niche Protein(TM) products and gene therapy.

     The Company's Gene Activation(TM) technology is a proprietary approach 
to the large scale production of therapeutic proteins which does not require 
the cloning of genes and their subsequent insertion into non-human cell 
lines. Consequently, the Company believes its Gene Activation technology 
avoids using patented approaches to protein production associated with such 
conventional genetic engineering techniques which have served as effective 
barriers to competition in the protein therapeutics market, which the Company 
estimates is a $15 billion market (1998 worldwide revenues).  As a result, 
the Company believes it will be able to develop and successfully 
commercialize a broad range of Gene Activated versions of proteins which have 
proven medical utility, received marketing approval from regulatory 
authorities and generated significant revenues in major markets.  The 
Company's most advanced Gene Activation development program is Gene Activated 
erythropoietin ("GA-EPO(TM)"), which Hoechst Marion Roussel, Inc. ("HMRI"), 
the Company's collaborative partner, advanced into Phase III trials in 
September 1998.  See "Item 3 -- Legal Proceedings."

     TKT's Niche Protein platform is based on protein replacement for the 
treatment of rare genetic diseases which are characterized by the absence of 
certain metabolic enzymes.  Since the defect in many of these disorders is 
understood in depth, product development pathways have the potential to be 
straightforward.  The Company believes that manufacturing and marketing of 
these products will require a relatively modest investment in infrastructure 
and plans to commercialize these products itself.  In December 1998, the 
Company, in collaboration with the National Institutes of Health, initiated a 
Phase II clinical trial of the alpha-galactosidase A protein ("alpha-gal") in 
patients with Fabry disease.

     The Company's gene therapy technology ("Transkaryotic Therapy(TM)") is a
non-viral, ex vivo system based on genetically modifying patients' cells to
produce and deliver therapeutic proteins for extended periods of time.  In
preclinical animal studies, the Company's Transkaryotic Therapy system has
produced target proteins at therapeutic levels for the lifetime of the
experimental animals.  In November 1998, the Company commenced a Phase I
clinical trial of TKT's gene therapy system for the long-term delivery of Factor
VIII for the treatment of hemophilia A.

GENE ACTIVATION: TECHNOLOGY BACKGROUND

     PROTEIN PRODUCTION: THREE TECHNOLOGICAL WAVES.  The therapeutic value of
certain proteins produced by the human body has been known for decades.  One of
the major advances in 20th-century medicine was the development of systems for
the large-scale production of therapeutic proteins outside the body. For
example, prior to the development of a manufacturing process for insulin more
than seventy years ago, patients with Type I (juvenile onset) diabetes were
offered no effective treatment and generally died of starvation at an early age.
Following the development of pharmaceutical insulin preparations for injection,
Type I diabetics could live long and relatively normal lives.  During this first
wave of protein production technology, proteins were generally purified from
human or animal tissue.  Insulin, for example, was isolated from the pancreas of
pigs and cattle, and growth hormone, for the treatment of short stature, was
isolated from the pituitaries of cadavers.

     During the second wave of protein production technology, based on the
cloning of human genes, proteins were manufactured using conventional genetic
engineering techniques.  As a result, by the mid-1980's, it became routine to
engineer cells to produce therapeutic proteins at levels that were substantially

<PAGE>

in excess of what could be obtained by purification from tissue.  However, since
many of the proteins produced by conventional genetic engineering techniques had
previously been purified, the patent protection afforded to this second wave of
protein production technology tended to focus on the genes encoding therapeutic
proteins.  Accordingly, many patents have been issued covering isolated and
purified DNA sequences encoding such proteins, various vectors used to insert
such DNA sequences into production cell lines, and cell lines modified by the
insertion of such DNA sequences.

     TKT believes its proprietary Gene Activation technology represents the
third wave in the evolution of protein production technology in that it is based
on the activation of genes encoding therapeutic proteins in human cells rather
than the cloning and transfer of these genes.  TKT's Gene Activation technology
avoids using the approach to protein production associated with the second wave.
The Company believes this will allow it to develop and commercialize a large
number of therapeutic proteins, including potentially improved versions of many
that are currently marketed.

     GENE STRUCTURE AND REGULATION OF GENE EXPRESSION.  Recent advances in
molecular biology, cell biology, and genomics have led to a much better
understanding of the structure and function of human genes than was possible
only a few years ago.  It is now generally accepted that virtually all genes
contain certain DNA sequences that provide information necessary for the cell to
assemble a specific sequence of amino acids that make up a protein ("coding DNA
sequences").  Thus each gene can be viewed as the blueprint for a particular
protein, and "gene expression" is the process which leads to the synthesis of
the protein it encodes.  Gene expression is controlled by certain DNA sequences
which function as switches that "turn on" the gene and trigger the synthesis of
the protein ("regulatory DNA sequences").  Despite the staggering variety of
proteins synthesized by the cells of the body, this process is universal.

     Essentially every human cell contains the same set of approximately 100,000
genes, but each cell type actually produces only a subset of the 100,000
proteins possible.  For example, although essentially all human cells contain
the insulin gene, only certain cells of the pancreas actually produce insulin.
The regulatory switches that turn on gene expression in the appropriate cell
type also turn off gene expression in all other cell types.  For this reason,
only pancreatic cells express insulin--the regulatory DNA sequences normally
associated with the insulin gene prevent expression elsewhere in the body.
TKT's Gene Activation technology is based on activating previously silent genes
by bypassing regulatory DNA sequences set in the "off position" with regulatory
DNA sequences set in the "on position."

     CONVENTIONAL RECOMBINANT PROTEIN PRODUCTION.  By the 1970's, the clinical
benefits of several proteins were well-known and the potential benefit of many
others was envisioned.  Based on a series of basic discoveries in the 1960's and
1970's, scientists learned to clone and manipulate genes of therapeutic
interest, leading directly to the birth of the biotechnology industry and the
large scale production of therapeutic proteins.  To produce large quantities of
a therapeutic protein using conventional genetic engineering techniques,
scientists first clone the relevant human gene by isolating the coding DNA
sequences for the gene from the human cell and transferring them to bacteria,
where large quantities of the gene are copied.  The cloned gene is then isolated
from the bacteria and placed in a test tube.  In this test tube, the cloned gene
is then fused to appropriate regulatory DNA sequences, and the resulting DNA
fragment containing both the regulatory DNA sequences and the coding DNA
sequences is inserted into a non-human (mammalian, yeast, or bacterial) cell.
This genetically modified cell is then propagated in large bioreactors for
commercial-scale production of the protein.

TKT'S GENE ACTIVATION TECHNOLOGY

     Although the conventional approach to recombinant protein production is
quite powerful, its use today faces certain commercial barriers and technical
limitations.  The primary barrier is that biotechnology companies have sought
and obtained patent protection covering many of the techniques used to produce
commercially-marketed proteins using conventional genetic engineering
techniques.


                                         -2-

<PAGE>

These patent rights have served as an effective entry barrier, minimizing
competition in the $15 billion protein therapeutics market (1998 worldwide
revenues).  In addition, conventional genetic engineering techniques for protein
production may face technical limitations arising from the need to first clone
the gene of interest.  For certain proteins, this step adds to development
times, increases costs and is technically challenging.  Technical difficulties
may also arise from the use of non-human production cell lines, which may result
in the production of proteins which may have therapeutically significant
differences from those naturally produced by the cells of the human body.
Furthermore, production processes based on conventional genetic engineering may
not have incorporated recent advances in cell culture systems with significant
efficiency and cost advantages as compared to processes originally developed
over a decade ago.

     To overcome these commercial barriers and technical limitations, TKT has
developed Gene Activation technology for the production of therapeutic proteins
that does not rely on the manipulation of cloned genes.  Using its proprietary
technology, TKT has succeeded in producing therapeutic proteins in human cells
by bypassing regulatory DNA sequences set in the "off position" with regulatory
DNA sequences set in the "on position" in order to activate the gene of
interest.  The Company's Gene Activation technology does not require the
manipulation of the protein coding DNA sequences of the gene.  The bypass of an
"off switch" with an "on switch" is accomplished by "gene targeting."

     Gene targeting is a technology by which DNA fragments can be "cut and 
pasted" precisely at pre-selected, desirable locations within the cell's 
genome. Gene targeting can be thought of as molecular surgery, with the 
surgical tools literally functioning at the molecular level.  The technical 
term for gene targeting, homologous recombination, reflects its underlying 
mechanism: cells have the capacity to align two homologous DNA sequences (two 
sequences that are quite similar) and exchange one with the other.  In Gene 
Activation, the new regulatory sequences are flanked with "homing" sequences 
and structural sequences which allow the cell to exchange the new active 
regulatory sequences in place of the old inactive ones.  The new sequences 
must be introduced precisely in order to allow the proper initiation of gene 
expression.

     In order to manufacture a protein of therapeutic interest using Gene
Activation, a human cell line producing the protein must be generated.  This
cell line will ultimately become the master cell bank for large scale
manufacturing and is generated as follows:

          1.   Determine the sequence of a portion of the regulatory DNA
               sequences that control the gene of interest;

          2.   Build a "targeting fragment" by fusing homing sequences to a new
               regulatory region known to be active in the human cell line
               chosen for manufacturing;

          3.   Introduce the targeting fragment into the cell line;

          4.   Identify and propagate an activated cell line producing the
               protein of interest; and

          5.   Optimize protein productivity and prepare the cell line for
               commercial scale manufacturing.

     The Company has successfully accomplished all of the steps described 
above for GA-EPO and its second, undisclosed Gene Activated product ("GA-II"). 
The results of TKT's work in this area have led to proof-of-concept that (i) 
gene targeting can be used to direct the integration of regulatory and 
structural sequences to a specific, pre-selected position in the genome, (ii) 
the product of the targeting event is a cell containing an activated gene and 
(iii) the protein production properties of cells created by Gene Activation 
are predictable and suitable for, and have been successfully used in, 
large-scale manufacturing.  Accordingly,

                                         -3-

<PAGE>

the Company believes that these methods may be used to express a wide variety of
therapeutically valuable proteins at levels suitable for large-scale
manufacturing purposes.  Because the Gene Activation process avoids many of the
technical limitations of conventional recombinant protein production technology,
the Company also believes that the Gene Activation process is at least as
efficient as, and may be more cost effective than, conventional genetic
engineering techniques for protein production.

TKT'S GENE ACTIVATION PRODUCTS

     The Company's initial strategy in exploiting its technology is to
commercialize Gene Activated proteins that have proven medical utility, have
received marketing approval from regulatory authorities and have achieved
significant revenues in major markets.  These protein products have experienced
high rates of acceptance among physicians and health care providers.  The
Company believes, based primarily on information obtained from annual reports of
public companies and other published sources, that the total sales of the ten
largest marketed proteins in 1998 was approximately $15 billion.  See Table I.
As the number of new approved protein products increases and as the number of
approved indications for such products increases, the Company believes that the
market for these protein products will continue to experience substantial
growth.  The Company also believes that the broad applicability of its Gene
Activation technology for protein production and the fact that many additional
proteins are currently in clinical development will provide a large number of
candidates for commercialization using TKT's Gene Activation technology.


      TABLE I.  COMPANY ESTIMATE OF 1998 WORLDWIDE PROTEIN PRODUCT REVENUES (IN
MILLIONS)

<TABLE>
<CAPTION>

 PROTEIN                    PRIMARY INDICATION               REVENUES
 -------                    ------------------               --------
 <S>                        <C>                              <C>
 Erythropoietin             Anemia                           $3,900
 Insulin                    Diabetes                          2,800
 G-CSF                      Neutropenia                       1,900
 Growth Hormone             Short stature                     1,500
 alpha Interferon           Hepatitis/Cancer                  1,300
 Factor VIII                Hemophilia A                      1,300
 beta Interferon            Multiple sclerosis                  800
 FSH                        Infertility                         800
 tPA                        Myocardial infarction               400
 Glucocerebrosidase         Gaucher disease                     400
</TABLE>

     TKT has focused its initial Gene Activation efforts on the development of
its GA-EPO product in collaboration with HMRI.  Erythropoiesis is the process by
which red blood cells (erythrocytes) are produced.  When the body requires
additional red blood cells, the kidney normally produces erythropoietin, a
circulating protein hormone which stimulates the differentiation of certain
progenitor cells in the bone marrow.  The kidney's critical role in red blood
cell production was determined in the 1950's, and erythropoietin was first
isolated and purified from the urine of patients with anemia in the 1970's (the
first wave).  The gene encoding erythropoietin was cloned in the 1980's and used
for production of the protein using conventional genetic engineering techniques
(the second wave).   Erythropoietins have been successfully used to treat anemia
associated with a variety of conditions, including the anemia of kidney failure
(which causes a reduction in the body's ability to produce the protein) and the
anemia of chemotherapy (which causes the destruction of a large number of bone
marrow progenitor cells).


                                         -4-

<PAGE>

     GA-EPO DEVELOPMENT STATUS.  TKT has successfully applied its Gene
Activation technology to produce GA-EPO in human cells (the third wave).  To
illustrate the underlying concept of the Gene Activation process, consider that
essentially all human cells contain the erythropoietin gene, yet only certain
cells of the kidney actually produce erythropoietin.  In all other cells in the
human body, the erythropoietin gene is inactive.  The erythropoietin gene is not
expressed in most human cells because regulatory sequences in those cells
prevent the protein from being made; the gene is controlled by a switch
("regulatory DNA sequences") that is permanently in the "off" position.  The
goal of TKT's GA-EPO program was to remove this "off switch" in a human cell in
which the erythropoietin gene is inactive and, in effect, replace it with
regulatory sequences comprising an "on switch" to activate erythropoietin
expression.

     TKT has generated a GA-EPO producing cell line that has been scaled up to
commercial production levels.  To accomplish this, TKT first studied the
regulatory region that prevents expression of the erythropoietin gene in most
human cells and developed an activation strategy.  Next, a targeting fragment
was constructed by fusing certain homing sequences to a new regulatory region
known to be active in the human cell line chosen for manufacturing.  The
targeting fragment was then introduced into the cell line under conditions
appropriate for homologous recombination to occur, and a resulting cell line
that produced GA-EPO was identified.  The GA-EPO productivity of the cell line
was optimized, and the cells were prepared for commercial-scale manufacturing.
The production process is at commercial scale and has been successfully used to
produce GA-EPO for clinical trials.

     The purified protein has been subjected to an extensive series of analyses
and has the properties expected of a human erythropoietin preparation.  In
particular, the protein has an appropriate molecular weight, amino acid
composition, amino acid sequence, secondary structure, and glycosylation
profile.  GA-EPO has been shown to function in vitro and in vivo in a
dose-dependent manner.  Finally, preclinical safety tests performed to date have
yielded satisfactory results.

     In a Phase I study completed in 1997 by HMRI, twelve healthy volunteers
were administered GA-EPO.  The goal of the study was to assess safety of GA-EPO
administration.  The study demonstrated that GA-EPO exhibited a satisfactory
safety profile and resulted in a dose-dependent increase in hematocrit.

     In 1998, HMRI completed a Phase II study of GA-EPO.  Thirty-two patients
with end stage renal disease were treated in two dosage groups.  The Phase II
trial resulted in no adverse events related to GA-EPO and demonstrated a
dose-dependent increase in hematocrit.

     In September 1998, HMRI commenced Phase III trials of GA-EPO, the goal of
which is to support a Biologics License Application ("BLA") for U.S. FDA
approval for the indications of renal failure in patients who are receiving
dialysis and in patients who are not yet undergoing dialysis.  Furthermore, the
clinical program has been designed to obtain FDA approval for intravenous and
subcutaneous administration of GA-EPO.  The program is expected to be completed
by the end of 1999.  During 1999, HMRI is expected to commence a Phase III trial
of GA-EPO for oncology related anemia.  GA-EPO is being reviewed within the FDA
by the Center for Biologics Evaluation and Research ("CBER").

     DEVELOPMENT STATUS OF OTHER GENE ACTIVATION PRODUCTS.  In collaboration 
with HMRI, TKT is developing GA-II.  HMRI accepted for development the Gene 
Activated cell line for GA-II in June 1997 and manufacturing is at commercial 
scale.  Pre-clinical testing is in progress, with satisfactory results 
achieved to date.  The Company expects HMRI to file an Investigational New 
Drug application ("IND") for this product in 1999.

                                         -5-
<PAGE>

     TKT's third Gene Activated protein ("GA-III") is in pre-clinical testing.
Manufacturing scale-up is in process, and the Company expects to file an IND for
this product in late 1999 or early 2000.  TKT is currently developing GA-III
independently.

     TKT believes that numerous development opportunities exist for Gene
Activated proteins.  In addition to the proteins discussed above, the Company is
currently developing four other Gene Activated proteins.  These programs are in
the research or pre-clinical stage.

GENE ACTIVATION COLLABORATIONS AND COMMERCIALIZATION STRATEGY

     In order to rapidly develop and exploit its Gene Activation technology, TKT
has entered into two strategic alliances with HMRI, the first in May 1994 and
the second in March 1995.  HMRI, with its affiliates, is one of the largest
pharmaceutical groups in the world, with significant distribution capabilities
in all major markets.  The alliances are focused on the development of two
products, GA-EPO and GA-II.

     Under two licenses agreements, HMRI was granted worldwide exclusive rights
to make, use and sell the two products.  HMRI is responsible, at its own
expense, for all worldwide development, manufacturing and marketing activities
for both products.   Pursuant to the agreement pertaining to GA-II, TKT also
granted HMRI an option to commercialize certain aspects of TKT's gene therapy
technologies.  As to both products, TKT has successfully generated cell lines
sufficient for scale-up to commercial production levels that have been accepted
and scaled up by HMRI.

     TKT has the potential to receive up to $125,000,000 ($58,000,000 for GA-EPO
and $67,000,000 for GA-II) from HMRI from the two alliances, consisting of
license fees, equity investments, milestones and research funding.  As of
December 31, 1998, TKT had received approximately $57,000,000  of such amount
(approximately $26,500,000 for GA-EPO and approximately $30,500,000 for GA-II).
The remaining payments are contingent upon the achievement of milestones in
connection with the continued development of these products.  TKT also is
entitled to royalties on sales of these two products.

     In December 1998, HMRI announced its intention to merge with Rhone-Poulenc
SA.  The merger is expected to be completed in 1999, subject to regulatory
approval, and will create the second largest global pharmaceutical company.

     Future Gene Activation products may include currently-marketed proteins,
proteins currently in late stage clinical development or proteins that are in
much earlier stages of development.  At present, TKT intends to focus on the
currently-marketed products until products from these latter two categories
demonstrate clinical and commercial viability.  TKT believes that its focus on
currently-marketed proteins for near-term commercialization and on
development-stage proteins for the long-term appropriately utilizes Company
resources, maximizes near-term commercial potential and will allow the Company
to build a strong Gene Activation product pipeline for the future.

NICHE PROTEIN(TM) PRODUCT DEVELOPMENT PLATFORM

     It is well established that certain genetic diseases are caused by the
deficiency of a single, well-defined protein.  Therefore, the most direct
approach to treatment is to manufacture the missing protein and administer it to
the patient.  TKT's Niche Protein development is focused on developing protein
replacement products to treat patients suffering from rare genetic diseases
characterized by protein deficiencies such as Fabry disease, Gaucher disease,
Hurler syndrome, Hunter syndrome, Pompe disease, and Tay-Sachs disease.

     Due to mutations in certain genes, individuals with these rare genetic
diseases are born lacking the ability to produce sufficient amounts of a
specific protein, resulting in symptoms which can be


                                         -6-
<PAGE>

debilitating and, ultimately, life threatening.  Unfortunately, no effective
treatment currently exists for most of these rare diseases.  The Company plans
to develop and commercialize products for a number of these diseases, with the
goal of reducing symptoms and potentially reversing progression of the disease.

TKT'S NICHE PROTEIN(TM) DEVELOPMENT PROGRAMS AND COMMERCIALIZATION STRATEGY

     The Company's product development strategy for its Niche Protein platform
is to leverage the Company's core competencies in gene expression, cell culture,
and protein characterization to create protein replacement products to treat
rare genetic diseases which are characterized by the absence of certain
metabolic enzymes.  Since the defects in many of the diseases which the Company
intends to address with its Niche Protein platform are understood in depth,
product development pathways have the potential to be straightforward.  The
Company is currently developing seven niche protein products, including
treatments for Fabry disease, Hunter syndrome, and Gaucher disease.

     The Company believes that it will be able to arrange for manufacturing of
its Niche Protein products under the terms of contract manufacturing agreements.
In addition, the Company believes that it will be able effectively to serve
Niche Protein markets with a small, focused sales force, thereby limiting the
Company's investment in sales and marketing infrastructure.  Thus, TKT views its
Niche Protein program as a nearer term opportunity to move into a series of
markets with a cost-effective, lower-risk approach and thereby build a
commercialization capability.  TKT expects to develop and commercialize these
products in the U.S. and Europe and obtain collaborative partners for Japan.

     FABRY DISEASE.  TKT's first target in the Niche Protein program is Fabry 
disease.  Fabry disease is an X-linked lysosomal storage disease caused by the 
deficiency of alpha-gal.  The disorder is characterized by the accumulation of 
lipids in lysosomes of vascular endothelial and smooth muscle cells and in a 
variety of other tissues.  Patients with classic Fabry disease of early onset, 
generally in adolescence, show diverse clinical manifestations including 
severe pain and cardiovascular and renal complications.  It is estimated that 
there are several thousand Fabry disease patients in the developed world.  
Current treatment of the disease is limited to the reduction of symptoms.  
Clinical trials of enzyme replacement therapy in the late 1970's have been 
reported using infusions of alpha-gal purified from placenta, spleen or 
plasma.  The intravenous injection of the enzyme resulted in the transient 
reduction in the plasma levels of the deleterious lipid.

     The Company believes that enzyme replacement therapy could result in an 
elimination of the medium- and long-term complications of the disease and in 
an increased life expectancy and improved quality of life.  In 1997, the 
Company, in collaboration with the National Institutes of Health under a 
collaborative research and development agreement ("CRADA"), conducted a Phase 
I clinical trial designed to characterize the safety and pharmacokinetic 
profile of alpha-gal.  Ten patients with Fabry disease were treated with a 
single dose of highly purified alpha-gal manufactured at TKT, with two 
patients treated at each of five escalating dose levels.  Plasma half-life and 
alpha-gal enzyme activity were examined before and after treatment, along with 
a series of clinical and laboratory safety assessments.  Nine out of ten 
patients showed a reduction of the toxic lipid that causes the symptoms of 
Fabry disease, with the reduction observed in both liver and kidney.  The 
treatment was well-tolerated, and no clinically significant side-effects were 
observed.  The half-life of the enzyme appears to support dosing at intervals 
of one week or longer.

     The Company initiated Phase II trials of its alpha-gal product in 
December 1998 with patients with Fabry disease.  The 24 patient, 
placebo-controlled trial is being conducted at the National Institutes of 
Health and is expected to be completed by the end of 1999.  The goal of the 
study is to assess safety and efficacy of the alpha-gal protein as a treatment 
for the disorder.

                                         -7-
<PAGE>

     The Company has received Fast Track designation for alpha-gal from the 
FDA; accordingly, the FDA is expected to review the Company's BLA within six 
months of submission.  TKT has also received Orphan Drug status for alpha-gal, 
potentially giving the Company a seven year market exclusivity in the U.S. 
following FDA approval.  The Company has entered into a contract manufacturing 
agreement to produce alpha-gal.  Development of a cell line for commercial 
manufacturing has been completed.

     In December 1998, the Company announced that it had entered into a
distribution agreement with Sumitomo Pharmaceuticals Co., Ltd. to commercialize
TKT's alpha-gal in Japan and other Asian territories.  Under the terms of the
agreement, Sumitomo paid TKT an upfront fee of $2,000,000 and is obligated to
make additional payments to TKT as the product moves through development and
commercialization.

     HUNTER SYNDROME.  TKT's second target in the Niche Protein platform is
Hunter syndrome.  Hunter syndrome is a X-linked lysosomal storage disorder
caused by a deficiency of the enzyme iduronate-2-sulphatase (I2S).  As a result
of this deficiency, complex carbohydrates accumulate in cells of the body,
causing debilitating symptoms in the patient.  Physical manifestations include
skeletal deformities, obstructive airway disease, cardiac failure and, in severe
cases, central nervous system involvement.  Cardiac and respiratory illness are
often the cause of death at an early age in patients with the disorder.  It is
estimated that there are several thousand Hunter syndrome patients in the
developed world.

     The Company believes that I2S enzyme replacement therapy could result in an
elimination of many of the clinical manifestations associated with Hunter
syndrome and an increased life expectancy and quality of life.  The Company
plans to file an IND covering its I2S product in late 1999 or early 2000.  The
Company has entered into a contract manufacturing agreement to produce I2S.  A
commercial quality cell line has been developed, and commercial scale up is
nearing completion.

GENE THERAPY TECHNOLOGY

     TKT'S GENE THERAPY APPROACH.  The first three waves of protein production
have a critical feature in common: regardless of methodology, the proteins are
manufactured outside the human body.  The Company believes that its approach to
gene therapy, Transkaryotic Therapy, represents the fourth wave of protein
production--a system that would restore the patient's natural ability to
produce a required therapeutic protein.

     TKT's approach to gene therapy is based on genetically modifying patients'
cells to produce and deliver therapeutic proteins for extended periods.  The
Company believes the approach will be safe, cost-effective and clinically
superior to the conventional delivery of proteins by injection.  In preclinical
animal studies, a single administration of one of the Company's gene therapy
products resulted in the lifetime production and delivery of therapeutic
proteins.

     TKT believes its gene therapy system is broadly enabling and, accordingly,
may be applicable to the treatment of a wide range of human diseases.  Because
TKT's gene therapy has demonstrated long-term delivery of therapeutic proteins
in animal model systems, the Company believes its approach may be well-suited to
the treatment of chronic protein deficiency states including hemophilia,
diabetes and hypercholesterolemia.  The diseases targeted by TKT are
characterized by a significant unmet medical need, and the clinical goals that
must be achieved by TKT's gene therapy products are well-defined.  The potential
benefits of TKT's gene therapy products include improved therapeutic outcome,
elimination of frequent painful injections and the problem of patient
compliance, a minimization of side effects due to over- or under-dosing of
conventional proteins and a reduction in costs.

     There are a large number of technical approaches to gene therapy, but two
basic distinctions can be used to characterize the field.  The first distinction
is viral versus non-viral.  Viral gene therapy


                                         -8-
<PAGE>

approaches use genetically modified viruses to introduce genes into human cells
by infection.  Non-viral approaches use noninfectious (chemical or physical)
means to introduce the genes.  The second distinction is in vivo versus ex vivo.
in vivo gene therapies are based on the administration of DNA-based drugs
directly to the patient.  ex vivo gene therapies are based on removing a small
number of cells from a patient, introducing a gene into the cells and implanting
the engineered cells into the patient.

     TKT's enabling gene therapy technology platform is a non-viral, ex vivo
system which the Company believes is significantly different from other
approaches to gene therapy.  The Company believes that these differences will
allow for physiologic levels of protein expression in patients for extended
periods, a goal that historically has represented a major obstacle in
alternative gene therapy systems.  The major alternative to TKT's system is
based on the use of genetically-modified retroviruses and adenoviruses to infect
patients' cells.  The Company believes that such viral ex vivo approaches
present a significant safety risk due to the possibility of causing new viral
infections in patients.  In addition, such approaches have not allowed long-term
production of the therapeutic protein in animal models or patients.

     To the best of the Company's knowledge, neither viral nor non-viral in vivo
gene therapy technologies have allowed long-term or high level protein
expression in the patient.  Accordingly, these technologies may be best-suited
for non-chronic applications, such as immunotherapy.  TKT believes Transkaryotic
Therapy is well-suited to allow safe and long-term delivery of therapeutic
proteins for the treatment of chronic protein deficiency states as demonstrated
by the long-term delivery of therapeutic proteins in animal models.

     In order to develop a safe, effective, non-viral, ex vivo gene therapy
system, the Company believes that several major tasks must first be accomplished
in basic and preclinical settings.  Each of the steps must be carried out to
allow the ultimate product to be manufactured efficiently, reproducibly and
cost-effectively, to be subjected to rigorous quality control to ensure safety
and to direct the long-term production and delivery of the therapeutic protein
in the patient.  The first step involves the development of techniques for
obtaining and propagating the cell types of interest.  Next, non-viral
methodologies must be developed that allow DNA fragments to be stably introduced
into these cells.  DNA fragments containing the appropriate DNA regulatory
sequences fused to the desired protein encoding sequences, for example, must be
constructed and introduced into cells to generate genetically-engineered cells
which express the therapeutic protein at clinically relevant levels.  After the
DNA fragments have been successfully introduced into human cells, methodologies
must then be developed which allow the engineered cells to properly process the
therapeutic protein.  The final step involves the development of methods and
formulations for the implantation of the engineered cells.

     TKT scientists have successfully accomplished all of the tasks set forth in
Table II and, in model systems, have successfully delivered therapeutic proteins
for the lifetime of the experimental animals.  Much of TKT's work has focused on
gene therapy using fibroblasts, a cell type present in the skin (and throughout
the body) that is readily obtained from patients and propagated in culture.  The
Company has developed a variety of methodologies for the stable transfection of
normal human cells.  "Stable transfection" means that the introduced DNA
fragment becomes part of a chromosome in the treated cell.  One such methodology
is electroporation, a technique based on subjecting cells to a brief electrical
pulse.  The pulse transiently opens small pores in the cell membrane that allow
the DNA fragments of interest to enter the cell.  The technique is simple,
reproducible (it works for a variety of cell types and for cells derived from
newborns to the elderly), efficient (one electroporation provides many more
transfected cells than required for treatment) and cost-effective (less than one
dollar per reaction).


                                         -9-
<PAGE>

TABLE II.  TKT'S GENE THERAPY SYSTEM: SUMMARY OF SELECTED TECHNICAL
ACCOMPLISHMENTS

<TABLE>
<CAPTION>

                    TASKS                                    ACHIEVEMENT                                      COMMENTS
                    -----                                    -----------                                      --------
 <S>                                         <C>                                               <C>
                                                                                              
 Cell types propagated                       Fibroblasts, myoblasts, mammary epithelial        Cells retain normal properties
                                             cells                                            
                                                                                              
 Proteins expressed                          Factor VIII, Factor IX, Growth Hormone,           All expressed at levels of at least 1
                                             Insulin, Interleukin-2, LDL receptor, alpha-gal   ug/million cells/day
                                                                                              
 Transfection methodologies applied          Electroporation, microinjection, polybrene        All with efficiencies greater than 1
                                             and calcium phosphate precipitation               stably transfected cell per thousand
                                                                                               treated cells
                                                                                              
 Proteins characterized                      Factor VIII, Factor IX, Growth Hormone,           All with natural post-translational
                                             alpha-gal                                             modifications
                                                                                              
 In vivo expression observed                 Factor VIII, Factor IX, Growth Hormone,           All at physiologic levels in animal
                                             Insulin                                           models
</TABLE>



     The Company believes it has developed the basic technologies required for a
safe and effective gene therapy approach which can be refined and optimized for
patient use.  In patients, TKT envisions that, in general, the system would
function as follows:

          1.   The clinician would identify the patient to be treated and
               perform a small skin biopsy.

          2.   In TKT's manufacturing facility, patient cells would be harvested
               from the biopsy specimen.

          3.   The DNA fragment containing DNA regulatory sequences and protein
               coding sequences would be introduced into the harvested cells by
               electroporation.  The DNA fragment and the electroporation
               methodology would be the same for all patients with a given
               disease.

          4.   A genetically-engineered cell expressing the therapeutic protein
               would be identified, propagated, subjected to appropriate
               characterization and quality control tests and formulated in a
               syringe.  The syringe would then be returned to the physician.

          5.   The physician would then inject the engineered cells under the
               patient's skin as an outpatient procedure.

     These patient techniques have been successfully carried out in an ongoing
Phase I clinical trial of growth hormone as a treatment for cachexia (described
below).  The procedures might vary based on the disease to be treated.  For
example, different cell types, sites of implantation and genes of interest could
be advantageous for a given disease.

     CLINICAL DEVELOPMENT STATUS.  The Company's first gene therapy clinical
trial is a Phase I study based on the implantation of genetically modified skin
fibroblasts to express growth hormone in cancer patients at risk for cachexia.
The principal purpose of this study is to determine the safety of the Company's
gene


                                         -10-
<PAGE>

therapy in humans.  At December 31, 1998, a total of 20 patients had been
enrolled in five escalating dosage blocks, with four patients per block.
Community physicians have injected the modified cells under the skin of
subjects; all patient procedures have been performed on an out-patient basis.
Preliminary data from this study suggests that the administration of the
genetically-engineered cells appears to be well-tolerated.    Prior to
proceeding with further clinical development (beyond Phase I) of this product,
the Company intends to seek a collaborative partner.

     In December 1998, the Company began the first clinical trial evaluating a
gene therapy treatment for hemophilia.  Twelve patients will be enrolled in the
Phase I safety study, which will be conducted at the Beth Israel Deaconess
Medical Center in Boston, Massachusetts.  The trial is expected to take up to
three years to complete, including a two year follow up period following the
treatment phase.

     The Company believes that Transkaryotic Therapy offers several clinical and
commercial advantages over conventional treatments and other gene therapies for
targeted diseases, including:

- -    SAFETY.  Transkaryotic Therapy does not use infectious agents such as
     retroviruses to genetically engineer the patient's cells.  TKT's non-viral
     method of producing genetically engineered cells allows for extensive
     safety testing prior to implantation of such cells in the patient.  In
     studies of TKT's gene therapy system involving over 5,000 animals, no side
     effects have been observed.

- -    LONG-TERM EXPRESSION.  Transkaryotic Therapy is designed to produce
     long-term results with a single treatment.  In preclinical animal studies,
     the Company has produced target proteins at therapeutic levels for the
     lifetime of the animals, suggesting the possibility of long-term
     effectiveness in humans.

- -    CONTROLLABILITY.  Transkaryotic Therapy is designed to deliver therapeutic
     proteins at levels which meet a patient's specific needs.  The Company
     believes that its gene therapy system will allow the physiologic and
     pharmacologic regulation of expression.  Further, the Company believes that
     the treatment afforded by Transkaryotic Therapy will be readily reversible
     so that therapy can be discontinued if no longer required.

- -    FLEXIBILITY.  The Company has focused on genetically-engineering a wide
     variety of human cell types because, although certain cell types are useful
     in the gene therapy of particular diseases, no single cell type is
     appropriate for the gene therapy of all diseases.

- -    EASE OF ADMINISTRATION.  Transkaryotic Therapy will allow for the
     administration of its products by a single injection under the patient's
     skin on an out-patient basis.  Furthermore, the potential long-term
     effectiveness of the treatment could eliminate problems of patient
     compliance.

- -    COST-EFFECTIVENESS.  Transkaryotic Therapy takes advantage of the patient's
     natural ability to synthesize therapeutic proteins for extended periods.
     The potential benefits of Transkaryotic Therapy include improved
     therapeutic outcome, the elimination of frequent painful injections and
     patient compliance problems, a reduction of side effects due to overdosing
     and underdosing of conventional proteins and significant reductions in
     cost.  Accordingly, the Company believes that its therapy may be less
     costly than therapy using conventional protein pharmaceuticals which
     require frequent administration.

TKT'S GENE THERAPY DEVELOPMENT PROGRAMS AND COMMERCIALIZATION STRATEGY

     The Company is focusing its development efforts on gene therapy products
for the treatment of chronic diseases with straightforward and
well-characterized etiologies.  For certain of these diseases, such as
hemophilia A, effectiveness, dose ranges and safety have been clearly
established in the context of

                                         -11-
<PAGE>

currently approved and marketed products.  For other diseases, preliminary in
vitro and animal model data strongly suggest that the long-term delivery of
appropriate therapeutic proteins will effectively treat the disease.  The
Company believes that this initial focus will provide strategic advantages by
allowing evaluation of Transkaryotic Therapy based on well understood clinical
parameters, thereby facilitating the regulatory approval process.  Furthermore,
the Company believes that when administered as part of its proprietary gene
therapy system, these proteins may provide therapeutic benefits not achievable
using conventional methods of delivery.

     HEMOPHILIA A.  When a blood vessel ruptures, an intricate series of events
allows the rapid formation of a clot in normal individuals.  One of the
best-studied coagulation disorders is hemophilia A, caused by a deficiency or
defect in protein coagulation Factor VIII.  Patients with the disease experience
acute, debilitating and often life-threatening bleeding episodes.  Depending on
the severity of the disease, bleeding may occur spontaneously or after minor
trauma.  Conventional treatment consists of temporarily increasing the patient's
Factor VIII levels through infusions of plasma-derived or recombinantly-produced
Factor VIII.  Factor VIII levels typically rise to therapeutic levels for only
two to three days following intravenous administration, then return to the
baseline subtherapeutic level, once again placing the patient at risk for a
serious bleeding episode.  It is estimated that there are about 19,000
hemophilia A patients in the U.S. and Canada, 25,000 in Europe, and 4,000 in
Japan.  In the U.S., an adult suffering from the disease receives Factor VIII
protein treatment only during bleeding crises at an average annual cost of
approximately $65,000.

     TKT's approach to the treatment of hemophilia A is based on the production
and delivery of Factor VIII using Transkaryotic Therapy.  The Company believes
that its Factor VIII gene therapy product has the potential to provide a
constant supply of therapeutic levels of the missing protein, effectively
eliminating the problem of rapid disappearance of the therapeutic protein.  The
Company has produced clonal populations of human fibroblasts which have been
transfected to express Factor VIII in vitro, demonstrated that the protein is
properly processed and achieved protein expression in animals.  As described
above, the Company commenced Phase I clinical trials of its gene therapy
approach for the long-term delivery of Factor VIII in November 1998.

     In July 1993, the Company entered into a Collaboration and License
Agreement with Genetics Institute, Inc. ("GI") relating to a joint development
and marketing program for a hemophilia A gene therapy product based on the
Company's non-viral technology.  The agreement provides that the parties will
collaborate to develop and commercialize a non-viral gene therapy product for
the treatment of hemophilia A using TKT's proprietary technology and GI's
patented Factor VIII genes.  Under the agreement, GI has granted TKT a
nonexclusive worldwide license under GI's patents covering truncated versions of
the gene encoding Factor VIII for use in certain non-viral gene therapy
applications.  GI has agreed to pay a portion of the clinical development costs
of the product in the U.S., Canada and the European Community.  TKT retained
exclusive manufacturing rights throughout the world and exclusive marketing
rights to all countries of the world except those in Europe.  Subject to certain
conditions, GI received exclusive rights to market the product in Europe.  The
agreement is terminable by GI in the event certain product development and
regulatory approval milestones are not reached.

     LONG-TERM GENE THERAPY TARGETS.  The Company's long-term gene therapy
product development strategy is focused on products for the treatment of
commonly occurring diseases, including both juvenile-  and adult-onset diabetes,
hypercholesterolemia and osteoporosis.  These are diseases for which either (i)
a proven therapeutic protein exists but effective treatment of the disease
requires complex patterns of regulation in the patient (for example, insulin is
widely used in the treatment of diabetes but delivery of insulin by conventional
methods is imprecise and does not prevent the serious complications of the
disease) or (ii) no protein has yet been proven effective in treating the
disease (for example, many proteins are thought to have potential in the
treatment of hypercholesterolemia, but that has yet to be proven conclusively in
patients).


                                         -12-
<PAGE>

     MANUFACTURING.  One of the critical aspects of any cell-based therapy is
the approach to manufacturing.  The manufacturing process takes up to six weeks.
It is essential to optimize the process to allow for a commercially-viable
product, and the Company believes it has accomplished such optimization.  To
produce early clinical materials, TKT has constructed a pilot manufacturing
facility designed to conform to FDA guidelines for Current Good Manufacturing
Practice ("cGMP").  For Phase III clinical trials and commercialization, TKT
intends to construct a cGMP-certified facility.

     The Company intends to manufacture its gene therapy products in central
manufacturing facilities.  Initially, the Company plans to construct a central
facility to serve the U.S.  As the Company's product pipeline matures, the
Company believes that demand will increase, possibly requiring the Company to
construct an additional manufacturing facility in the U.S.  Other gene therapy
companies have adopted a strategy based on locating a cell processing facility
in every large city (or potentially large hospital).  TKT believes that the
requirements for strict quality control and the benefits of economy of scale are
better achieved using the central manufacturing strategy.

PATENTS, PROPRIETARY RIGHTS AND LICENSES

     PROPRIETARY ISSUES.  For many currently marketed proteins, the product
manufactured using conventional genetic engineering techniques does not
represent the first time the protein was isolated and purified.  As such, it was
generally not possible to obtain a broad composition of matter patent for many
of the currently marketed proteins.  In contrast, the isolated and purified DNA
sequences encoding these proteins, various vectors used to insert such DNA
sequences into production cell lines, cell lines modified by the insertion of
such DNA sequences, and corresponding methods (including methods of producing
proteins using this approach) led to issued patents in many cases.  TKT believes
that, by completely avoiding the use of isolated and purified DNA sequences
encoding proteins of commercial interest, the Company's technology does not
infringe claims based on isolated and purified DNA sequences encoding such
proteins.  Furthermore, the Company intends to avoid the use of technologies
(such as specific protein purification procedures) that are the subject of
patents that are not limited to protein products manufactured using conventional
genetic engineering techniques.

     Over the past decade, there has been a dramatic increase in the number of
approaches to gene therapy under development in both academic and industrial
laboratories.  A large number of patent applications have been filed in the U.S.
and worldwide relating to this work, and a number of gene therapy patents have
issued to date.  The Company requested, and the U.S. Patent and Trademark Office
(the "PTO") declared in January 1996, an interference regarding an issued patent
with broad claims to ex vivo gene therapy.  The participants in the interference
are TKT, Genetic Therapy, Inc. (a wholly-owned subsidiary of Novartis AG),
Syntex (U.S.A.) (a wholly-owned subsidiary of Roche Holdings, Inc.), and Somatix
Therapy Corporation ("Somatix").  Somatix subsequently merged into Cell Genesys,
Inc.  With the possible exception of the patent involved in the interference,
the Company believes its Transkaryotic Therapy technology does not infringe on
patents issued to date.

     The PTO proceeding will determine the patentability of the subject matter
of the interference and which of the parties first developed this subject
matter.  The process to resolve the interference can take many years.  The
outcome of interferences can be quite variable: for example, none of the four
parties may receive the desired claims, one party may prevail, or a settlement
involving two or more of the parties may be reached.  There can be no assurance
that TKT will prevail in this interference or that, even if it does prevail, the
Company can meaningfully protect its proprietary position.

     In the event TKT does not prevail, a January 1997 Federal Trade Commission
("FTC") decision may then be relevant.  The FTC entered a consent order to
resolve anticompetitive concerns raised by the merger of Ciba-Geigy Limited and
Sandoz Limited into Novartis AG.  As part of the consent order, the constituent
entities of Novartis will be required to provide all gene therapy researchers
and developers



                                         -13-
<PAGE>

with non-exclusive licenses to the patent upon which Novartis is involved in the
interference.  The Company has entered into an agreement with Somatix under
which the Company's ability to market its non-viral gene therapy products will
not be affected should Somatix win the interference.

     At December 31, 1998, the Company had six issued U.S. patents and 28
pending patent applications in the U.S. to protect its proprietary methods and
processes.  It has also filed corresponding foreign patent applications for
certain of these U.S. patent applications.  The issued U.S. patents and patent
applications relate to the Gene Activation platform in general, DNA sequences
required for Gene Activation, vectors required for Gene Activation, cells
modified by Gene Activation, proteins produced by Gene Activation, corresponding
Gene Activation methods, the Transkaryotic Therapy platform in general, the
Niche Protein Platform in general, methods of propagating and transfecting
cells, methods for obtaining expression of therapeutic proteins and homologous
recombination in cells, and cells modified by the preceding methods.

     The Company believes that protection of the proprietary nature of its
products and technology is important to its business.  Accordingly, it has
adopted and will maintain a vigorous program to secure and maintain such
protection.  The Company's practice is to file patent applications with respect
to technology, inventions and improvements that are important to its business.
The Company also relies upon trade secrets, unpatented know-how, continuing
technological innovation and the pursuit of licensing opportunities to develop
and maintain its competitive position.  There can be no assurance that others
will not independently develop substantially equivalent proprietary technology
or that the Company can meaningfully protect its proprietary position.

     As a general matter, patent positions in the fields of biotechnology and
biopharmacology are highly uncertain and involve complex legal, scientific and
factual matters.  To date, there has emerged no consistent policy regarding the
breadth of claims allowed in biotechnology patents.  Consequently, although TKT
plans to prosecute aggressively its applications and defend its patents against
third parties, there can be no assurance that any of the Company's patent
applications relating to the technology used by the Company will result in the
issuance of patents or that, if issued, such patents or the Company's existing
patents will not be challenged, invalidated or circumvented or will afford the
Company protection against competitors with similar technology.   Any litigation
or interference proceedings regarding patent or other proprietary rights may
result in substantial cost to the Company, regardless of outcome, and, further,
may adversely affect TKT's ability to develop, manufacture and market its
products and to form strategic alliances.

     The Company's technologies and potential products may conflict with patents
which have been or may be granted to competitors, universities or others.  As
the biotechnology industry expands and more patents are issued, the risk
increases that the Company's technologies and potential products may give rise
to claims that they infringe the patents of others.  Such other persons could
bring legal actions against the Company claiming damages and seeking to enjoin
commercialization of a product or use of a technology.  If any such actions are
successful, in addition to any potential liability for damages, the Company
could be required to obtain a license in order to continue to use such
technology or to manufacture or market such product or could be required to
cease using such product or technology.  There can be no assurance that the
Company would prevail in any such action or that any license required under any
such patent would be made available or would be made available on acceptable
terms.  The Company believes that there may be significant litigation regarding
patent and other intellectual property rights in the fields of all three of its
product platforms.

     In April 1997, Amgen Inc. ("Amgen") filed a civil action in the U.S.
District Court in Massachusetts against the Company and HMRI relating to GA-EPO
and the processes for producing GA-EPO.  See "Item 3 - Legal Proceedings."


                                         -14-
<PAGE>

     To further protect its trade secrets and other proprietary property, the
Company requires all employees, Scientific Advisory Board members, consultants
and collaborators having access to such proprietary property to execute
confidentiality and invention rights agreements in favor of the Company before
beginning their relationship with the Company.  While such arrangements are
intended to enable the Company to better control the use and disclosure of its
proprietary property and provide for the Company's ownership of proprietary
technology developed on its behalf, they may not provide meaningful protection
for such property and technology in the event of unauthorized use or disclosure.

     LICENSING.  The Company has entered into several licensing agreements under
which it has acquired certain worldwide rights to use proprietary genes and
related technology in its non-viral gene therapy products.  In particular, the
Company has a nonexclusive license for certain non-viral gene therapy
applications from GI with respect to GI's patented Factor VIII genes and a
nonexclusive sublicense for non-viral gene therapy applications from British
Technology Group plc ("BTG") with respect to BTG's patented Factor IX gene.  In
addition, the Company has an exclusive license to certain pending and issued
patents from Women's and Children's Hospital, North Adelaide, Australia related
to certain mucopolysaccharidoses (MPS), including Hurler and Scheie syndrome
(MPS I), Hunter syndrome (MPS II) and Sanfilippo syndrome (MPS III).  TKT's
rights under these gene licenses and sublicenses are for the term of the last to
expire patent included in the licensed patent rights.  Although the Company is
not currently in default under any of these agreements, there can be no
assurance that such defaults will not occur in the future.  Should such a
default occur and any of these licenses or sublicenses be terminated in the
future, the Company could lose the right to continue to develop one or more of
its potential products, which loss could have a material adverse effect upon the
Company's business.

COMPETITION

     The Company believes that the primary competitive factors relating to the
products that it is developing include safety, efficacy, reliability,
distribution channels and price, and disease management services.  In addition,
the length of time required for products to be developed and to obtain
regulatory and, in some cases, reimbursement approval are important competitive
factors.  The biotechnology industry is characterized by rapid and significant
technological change.  Accordingly, the Company's success will depend in part on
its ability to respond quickly to medical and technological changes through the
development and introduction of new products.  The Company believes it competes
favorably with respect to these factors, although there can be no assurance that
it will be able to continue to do so.

     Many of the Company's competitors have substantially greater financial and
other resources than the Company, including larger research and development
staffs and more experience and capabilities in conducting research and
development activities, testing products in clinical trials, obtaining
regulatory approvals and manufacturing, marketing and distributing products.
Smaller companies may obtain access to such skills and resources through
collaborative arrangements with pharmaceutical companies or academic
institutions.

     There can be no assurance that TKT will succeed in developing and marketing
technologies and products that are more clinically efficacious and
cost-effective than existing established treatments or new approaches and
products developed and marketed by competitors.  The development by others of
alternative or superior treatment methods could render the Company's products
obsolete or noncompetitive with respect to some or all of the competitive
factors described above.  In addition, treatment methods not clearly superior to
the Company's could achieve greater market penetration through competitors'
superior sales, marketing or distribution capabilities.

     The Company's competitive position also depends upon its ability to attract
and retain qualified personnel, obtain patent protection, secure licenses of
necessary genes and technology from third parties,



                                         -15-
<PAGE>

or otherwise develop proprietary products or processes and secure sufficient
capital resources for the typically substantial expenditures and period of time
prior to commercial sales of each product.

     GENE ACTIVATION.  At present, the Company considers its primary competition
with respect to its Gene Activation technology to be companies involved in the
current production of therapeutic proteins.  These companies have obtained
patent protection covering many of the techniques used to produce
commercially-marketed proteins using conventional genetic engineering
techniques.  These patent rights have served as an effective entry barrier in
the $15 billion protein therapeutics market (1998 worldwide revenues).  Several
pharmaceutical and biotechnology companies have an established presence in the
field of therapeutic protein production.  For example, erythropoietin is
marketed by Johnson & Johnson ("J&J") and Amgen in the U.S.; by Boehringer
Mannheim GmbH and J&J in Europe; and by Sankyo Company Ltd. and Chugai
Pharmaceutical Co., Ltd. in Japan.

     NICHE PROTEINS.  For many of the disease targets of the Company's Niche
Protein program, there is currently no cure or effective treatment.  Treatments
are generally focused on the management of the disease's clinical symptoms,
particularly pain.  In general, the Company believes that these diseases may
represent markets too small to attract the resources of larger pharmaceutical
companies, but provide attractive commercial opportunities to smaller
companies, such as TKT.  The Company believes its major competition with respect
to Fabry disease and Gaucher disease to be Genzyme Corporation.

     The Orphan Drug Act of 1983 generally provides incentives to manufacturers
to undertake development and marketing of products to treat relatively rare
diseases or diseases where fewer than 200,000 persons in the United States at
the time of application for Orphan Drug designation would be likely to receive
the treatment.  The Company believes that many of the potential products in its
Niche Protein program will qualify as Orphan Drugs and intends to pursue Orphan
Drug  designations, where appropriate. A drug that receives Orphan Drug
designation by the FDA and is the first product to receive FDA marketing
approval for its stated product claim is entitled to a seven-year exclusive
marketing period in the United States for that product claim.

     There can be no assurance, however, that other companies will not seek an
Orphan Drug designation and obtain FDA marketing approval for a product
competitive with a Niche Protein product before the Company obtains such
approval.  If another company obtains Orphan Drug marketing approval and
receives seven-year marketing exclusivity, it is possible that the Company would
not be permitted by the FDA to market a similar product in the United States
during the exclusivity period.

     GENE THERAPY.  The Company's gene therapy system will have to compete with
other gene therapy systems as well as with conventional methods of treating the
diseases and conditions targeted by the Company and new non-gene therapy
treatments which may be developed in the future.  A number of commercial
entities, including major established biotechnology and pharmaceutical
companies, as well as development stage entities, currently are involved in the
field of human gene therapy.

GOVERNMENT REGULATION

     All of the Company's products will require regulatory approval by U.S. and
foreign government agencies prior to commercialization in such countries.  In
particular, protein therapeutics are subject to rigorous preclinical and
clinical testing, and other pre-market approval procedures administered by the
FDA and similar authorities in foreign countries.  In addition, gene therapy is
a new technology, and regulatory approvals may be obtained more slowly than for
products produced using conventional technologies.  In the U.S., various federal
and in some cases, state and local statutes and regulations also govern or
influence the manufacturing, labeling, storage, record keeping and marketing of
such products.



                                         -16-
<PAGE>

     Obtaining approval from the FDA and other regulatory authorities for a
therapeutic product may take several years and involve substantial expenditures.
Moreover, ongoing compliance with applicable requirements can entail the
expenditure of substantial resources.  Difficulties or unanticipated costs may
be encountered by the Company in its efforts to secure necessary governmental
approvals, which could delay or preclude the Company from marketing its
products.

     The activities required before a new pharmaceutical agent may be marketed
in the U.S. begin with preclinical testing.  Preclinical tests include
laboratory evaluation and animal studies to assess the potential safety and
efficacy of the product.  The results of these studies must be submitted to the
FDA as part of an IND, which must be reviewed and cleared by the FDA before
proposed clinical testing can begin.  Clinical trials are conducted in
accordance with specific federal regulations (known as Good Clinical Practices).
The clinical protocols detail the objectives of the study, the parameters to be
used to monitor safety and the efficacy criteria to be evaluated.  Each clinical
protocol must be submitted to the FDA as part of an IND.  Further, each clinical
study must be conducted under the auspices of an independent IRB at the
institution at which the study will be conducted.  Each IRB will consider, among
other things, ethical factors, the safety of human subjects, and informed
consent.

     Clinical trials are typically conducted in three sequential phases.  In
Phase I, clinical trials typically include a small number of subjects (often
healthy volunteers) to determine the early safety profile and the pattern of
drug distribution and metabolism.  In Phase II, clinical trials are conducted
with larger groups of patients afflicted with a specific disease in order to
further test safety and determine optimal dose amounts, dose schedules, and
routes of drug administration.  In Phase III, larger-scale, multi-center,
comparative clinical trials are conducted with patients afflicted with a target
disease in order to provide enough data for a valid statistical test of efficacy
and safety required by the FDA and others.  In the case of products for
life-threatening disease, the initial human testing may be done in patients
rather than healthy volunteers.  Since these patients are already afflicted with
the target disease, it is possible that such studies may provide results
traditionally obtained in Phase II trials.  These trials are frequently referred
to as Phase I/II trials.  Although some of the Company's products are being
considered for patients with life-threatening diseases, there can be no
assurance that the FDA will allow Phase I/II studies, or that if Phase I/II
studies are permitted, that this study design would shorten the development time
for any of the Company's products.  The FDA receives reports on the progress of
each phase of clinical testing, and it may require the modification, suspension,
or termination of clinical trials if, among other things, an unreasonable risk
is presented to patients, or if the design of the trial is insufficient to meet
its stated objective.

     After completion of clinical trials of a new product, FDA marketing 
approval must be obtained.  License applications submitted to the FDA have 
historically taken two to five years to receive approval.  The Company expects 
that its products will be regulated as biologics.  Traditionally, both a 
Product License Application and an Establishment License Application have been 
required prior to commercial marketing.  The FDA will be proposing regulations 
to implement the new BLA provision in the Food and Drug Administration 
Modernization Act of 1997 (the "Act"), which allows for a single license 
application.  The Act sets as a goal for the FDA, but does not require the 
review and action on  a complete license application within 12 months.  In 
addition, if the FDA determines that a product would be a significant 
improvement in the safety or effectiveness of the treatment, diagnosis or 
prevention of a serious or life threatening disease, the FDA may designate the 
product for priority review, in which case the FDA's  goal is to review and 
act on the complete license application within six months of the submission 
date.  To the extent one of the Company's products might fall within the 
existing or future BLA regulations for certain enumerated biotechnology 
products, these regulations may provide guidance regarding FDA expectations.  
If the FDA determines that an application is incomplete, or that important 
issues are unanswered by the data in the application, approval times could be 
delayed significantly.  Notwithstanding the submission of relevant data, the 
FDA may ultimately decide that the license application does not satisfy its 
criteria for approval.

                                         -17-
<PAGE>

     Even if FDA clearances are obtained, a marketed product is subject to
continual review.  Later discovery of previously unknown problems or failure to
comply with the applicable regulatory requirements may result in restriction on
the marketing of a product or withdrawal of the product from the market as well
as possible civil or criminal sanctions.  In addition, the manufacturing
facility for the Company's products will be subject to FDA inspection for
adherence to cGMP prior to marketing clearance and periodically following
approval.  This will require the Company to observe rigorous manufacturing
specifications.

     The Company believes that many of its Gene Activation products are likely
to be reviewed within the FDA by CBER.  CBER currently has no "bioequivalence"
pathway for the rapid approval of closely-related biologics.  The Company
believes that its Gene Activated products will be treated as new biologic
entities and require a complete regulatory and clinical program.  However, these
programs may have the advantage of focusing on Gene Activated products with
conventional, previously approved, counterparts that are well-known to
regulatory authorities around the world (in contrast to a typical new biologic,
which has no related history concerning its safety and efficacy in humans).

     In April 1996, the FDA issued a document entitled "FDA Guidance Concerning
Demonstration of Comparability of Human Biological Products, Including
Therapeutic Biotechnology-derived Products." This document describes situations
in which a manufacturer can make manufacturing changes and  establish the
comparability of the product using physical, chemical, bioassay, preclinical
animal and/or pharmacological methods, without the need for additional clinical
trials.

     In addition to regulations enforced by FDA, the Company is also subject to
regulation under the Occupational Safety and Health Act, the Environmental
Protection Act, the Toxic Substances Control Act, the Resource Conservation and
Recovery Act and other present and potential future federal, state or local
regulations.  The Company's research and development involves the controlled use
of hazardous materials, chemicals, biological materials and various radioactive
compounds.  Although the Company believes that its safety procedures for
handling and disposing of such materials comply with the standards prescribed by
state and federal regulations, the risk of accidental contamination or injury
from these materials cannot be completely eliminated.  In the event of such an
accident, the Company could be held liable for any damages that result and any
such liability could exceed the resources of the Company.

     For marketing outside the U.S., the Company also is subject to foreign
regulatory requirements governing human clinic trials and marketing approval for
products.  The requirements governing the conduct of clinical trials, product
licensing, pricing and reimbursement vary greatly from country to country.

EMPLOYEES

     As of December 31, 1998, the Company had 178 full-time employees, including
155 in research and development.  The Company's employees are not covered by any
collective bargaining agreement.  TKT considers relations with its employees to
be good.

TRADEMARKS

     TRANSKARYOTIC THERAPIES(TM), TKT(TM), TRANSKARYOTIC THERAPY(TM), 
NICHE PROTEIN(TM), GA-EPO(TM), GENE ACTIVATED(TM), and GA(TM) are 
trademarks of the Company.

                                         -18-
<PAGE>

ITEM 2.   PROPERTIES

     The Company leases a total of approximately 108,000 square feet of
laboratory and office space in buildings located in Cambridge, Massachusetts.
These facilities include pilot facilities for gene therapy and protein product
manufacturing.

     The Company's current facilities may not be adequate to accommodate the
Company's needs beyond 2000.  The Company currently expects to meet its
facilities requirements through development of a new facility or conversion of
an existing building.  The Company expects to seek financing for all or a
significant portion of the cost of any new facility.

ITEM 3.   LEGAL PROCEEDINGS

     In April 1997, Amgen filed a civil action in the U.S. District Court in
Massachusetts against the Company and HMRI, the Company's collaborative partner.
The complaint in the action alleges that the Company's Gene Activated
erythropoietin product ("GA-EPO") and processes for producing GA-EPO infringe on
Amgen's U.S. Patent Numbers 5,547,933, 5,618,698, and 5,621,080 and requests
that TKT and HMRI be enjoined from making, using, or selling GA-EPO and that the
court award Amgen monetary damages.  In November 1997, TKT and HMRI filed a
Motion for Summary Judgment.  On the same date, Amgen filed a Motion for Summary
Judgment of Infringement.  TKT and HMRI opposed that motion, stating that there
has been no infringement.

     In April 1998, the U.S. District Court granted TKT and HMRI's Motion for
Summary Judgment and denied Amgen's Motion for Summary Judgment on the ground
that all of TKT and HMRI's GA-EPO related activities to that date had been
solely for uses reasonably related to the production of information for
submission to the FDA for regulatory approval and, under the Hatch-Waxman Act,
do not constitute acts of patent infringement.  The Court ordered Amgen's
remaining claim for declaratory judgment of future infringement administratively
closed, to be reopened upon motion of either party for good cause shown.  The
Court also stated that issuance by the FDA of a product license presumably would
constitute good cause to reopen that claim.  Finally, the Court stated that,
should the case be reopened and should Amgen seek preliminary equitable relief,
the Court will combine any hearing on a preliminary injunction with trial on the
merits.  The Company expects that the case will be reopened.

     Should the case be reopened, the Company can provide no assurance as to the
outcome of this litigation.  A decision by the court in Amgen's favor, including
the issuance of an injunction against the making, use or sale of GA-EPO by the
Company and HMRI in the United States, or any other conclusion of the litigation
in a manner adverse to the Company and HMRI, would have a material adverse
effect on the Company's business, financial condition, and results of
operations.

     Pursuant to the Amended and Restated License Agreement, dated March 1995,
by and between HMRI and the Company, HMRI assumed the cost of defense of the
suit by Amgen.  The Company will reimburse HMRI for the Company's share of
litigation expenses, as defined, from future royalties, if any, received from
the sale of GA-EPO and in certain other circumstances.

     There can be no assurance that the Company will not in the future become
subject, in the United States or any other country, to additional patent
infringement claims, interferences and other litigation involving patents, or
any patents that may issue on any pending patent applications, including Amgen
patent applications.


                                         -19-
<PAGE>

     The Company is currently involved in a patent interference proceeding
before the PTO involving a patent and several patent applications in the gene
therapy field.  See "Item 1 - Business--Patents- Proprietary Rights and
Licenses."

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

     No matters were submitted to a vote of security holders during the fourth
quarter of the fiscal year covered by this report.


EXECUTIVE OFFICES OF THE REGISTRANT

         The executive officers of the Company are as follows:

 Name                            Age   Position held with the Company
 ----                            ---   ------------------------------

 Richard F Selden, M.D., Ph.D.   40    President, Chief Executive Officer

 Douglas A. Treco, Ph.D.         41    Senior Vice President, Research and
                                       Development

 Christoph M. Adams, Ph.D.       42    Vice President, Business Development

 Daniel E. Geffken               42    Vice President, Finance, Chief Financial
                                       Officer and Secretary

 Kurt C. Gunter, M.D.            44    Vice President, Clinical and Regulatory
                                       Affairs

     Each officer's term of office extends until the first meeting of the Board
of Directors following the next annual meeting of stockholders and until a
successor is elected and qualified.

     Richard F Selden, M.D., Ph.D. is the founder of TKT.  He has served as
Chief Scientific Officer, Chairman of the Scientific Advisory Board and a
Director since the Company's inception in 1988 and as President and Chief
Executive Officer since June 1994.  Prior to founding TKT, Dr. Selden was an
Instructor in pediatrics at Harvard Medical School.  He received an A.B. in
Biology from Harvard College, an A.M. in Biology from the Harvard University
Graduate School of Arts and Sciences, a Ph.D. in genetics from the Division of
Medical Sciences at Harvard Medical School and an M.D. from Harvard Medical
School.

     Douglas A. Treco, Ph.D. has directed research at the Company since its
inception in 1988.  Since February 1997, he has served as the Senior Vice
President, Research and Development and from June 1993 to February 1997, he
served as Vice President, Director of Research and Development.  Prior to
joining the Company, Dr. Treco was a Research Fellow in Genetics, Department of
Molecular Biology, Massachusetts General Hospital and Department of Genetics,
Harvard Medical School.  He received a B.S.  in Biology and Chemistry from the
University of Delaware and a Ph.D. in Biochemistry and Molecular Biology from
the State University of New York, Stony Brook.

     Christoph M. Adams, Ph.D. has served as Vice President, Business
Development of the Company since March 1994.  From May 1991 to February 1994,
Dr. Adams was Business Development Manager at the Pharmaceuticals Division of
Ciba-Geigy AG in Basel, Switzerland.  Dr. Adams received a Ph.D. in Organic
Chemistry from the University of Zurich and a M.B.A. from INSEAD, Fontainebleau,
France.


                                         -20-
<PAGE>

     Daniel E. Geffken has served as Vice President, Finance and Chief Financial
Officer of the Company since February 1997.  From June 1993 to February 1997,
Mr. Geffken was Chief Financial Officer of CytoTherapeutics, Inc., a
biotechnology company, and from December 1995 to February 1997, he served as
Vice President.  He received a B.S.  in Economics from The Wharton School,
University of Pennsylvania and a M.B.A. from the Harvard Business School.

     Kurt C. Gunter, M.D. has served as a consultant to the Company since
September 1993 and as Vice President, Clinical and Regulatory Affairs since July
1996.  From September 1993 to June 1996, Dr. Gunter worked in the Department of
Laboratory Medicine at Children's National Medical Center, most recently as
Director of Stem Cell Processing, Hematology and Blood Donor Center.  He
received a B.S. in Biological Sciences from Stanford University and an M.D. from
the University of Kansas School of Medicine.

                                      PART II

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

     The Company's Common Stock commenced trading on October 17, 1996 on the
Nasdaq National Market under the symbol "TKTX."  As of March 5, 1999, there were
165 holders of record of the Company's Common Stock.

     The following table sets forth for the fiscal periods indicated the range
of high and low closing prices for the Company's Common Stock on the Nasdaq
National Market.

<TABLE>
<CAPTION>

                                                            HIGH        LOW
                                                         ----------   --------
<S>                                                      <C>          <C>
1998
QUARTER ENDED:
  December 31 . . . . . . . . . . . . . . . . . . . . .  $ 25 15/16   $ 15 1/8
  September 30  . . . . . . . . . . . . . . . . . . . .    30           19 1/8
  June 30 . . . . . . . . . . . . . . . . . . . . . . .    36           25 3/4
  March 31  . . . . . . . . . . . . . . . . . . . . . .    39 1/8       29
1997
QUARTER ENDED:
  December 31 . . . . . . . . . . . . . . . . . . . . .  $ 43 1/4     $  27
  September 30  . . . . . . . . . . . . . . . . . . . .    44 3/4        27 3/4
  June 30 . . . . . . . . . . . . . . . . . . . . . . .    32 1/4        12 3/4
  March 31  . . . . . . . . . . . . . . . . . . . . . .    25 3/4        17
</TABLE>

     The Company has never declared or paid any cash dividends on its capital
stock.  The Company currently anticipates that it will retain all future
earnings, if any, to fund the development and growth of its business and does
not anticipated paying any cash dividends on its Common Stock in the foreseeable
future.


                                         -21-
<PAGE>

ITEM 6.   SELECTED FINANCIAL DATA

     The following selected consolidated financial data of the Company for the
five years ended December 31, 1998 are derived from the consolidated financial
statements of the Company.  The information set forth below should be read in
conjunction with "Management's Discussion and Analysis of Financial Condition
and Results of Operations" included as Item 7 and the consolidated financial
statements and related footnotes included as Item 8 in this Form 10-K.

<TABLE>
<CAPTION>

                                                                YEAR ENDED DECEMBER 31,

 (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)              1998       1997      1996       1995      1994
 <S>                                                 <C>        <C>        <C>        <C>       <C>
     STATEMENT OF OPERATIONS DATA

 License and research revenues                       $  5,325   $  5,788   $  4,225   $ 15,400  $ 10,000

 Research and development expenses                     25,617     18,111     14,019     10,529     9,126

 Net income (loss)                                    (19,965)   (12,871)   (11,972)     2,074    (3,422)

 Basic net income (loss) per share (pro forma in        (1.05)     (0.74)     (0.98)      0.19
   1996 and 1995)

 Shares used to compute basic net income (loss) per    19,052     17,394      12,262    10,862
   share (pro forma in 1996 and 1995)
</TABLE>

<TABLE>
<CAPTION>

                                                                       December 31,

 (IN THOUSANDS)                                        1998       1997      1996       1995      1994
 <S>                                                 <C>        <C>        <C>        <C>       <C>
     BALANCE SHEET DATA

 Cash and marketable securities                     $110,155    $129,554   $ 86,255    $ 34,485  $  7,579

 Total assets                                        117,962     134,948     90,998      39,218    13,472

 Redeemable preferred stock                               --          --         --       4,440     4,230

 Total stockholders' equity                          113,646     131,749     89,644      33,541     7,073
</TABLE>


     The Company has implemented Statement of Financial Accounting Standards No.
128, "Earnings Per Share", which requires the presentation of both basic and
diluted earnings per share in the Consolidated Statements of Operations.  The
per share amounts presented above and in Item 7, "Management's Discussion and
Analysis of Financial Condition and Results of Operations", are based on the
basic weighted average shares outstanding unless specifically identified as
diluted.


                                         -22-
<PAGE>

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

OVERVIEW

     Since its inception in 1988, Transkaryotic Therapies, Inc. (the "Company")
has been primarily engaged in the development and commercialization of products
based on the Company's three proprietary development platforms: Gene Activated
proteins, Niche Protein products and gene therapy.  No revenues have been
derived from the sale of any products, and the Company does not expect to
receive revenues from product sales until at least 2000.  The Company expects
that its research and development expenditures will increase substantially in
future years as product development efforts accelerate.  With the exception of
1995, the Company has incurred substantial annual operating losses since
inception and expects to incur substantial operating losses in the future.  At
December 31, 1998, the Company's accumulated deficit was $69,952,000.  As a
result, the Company is dependent upon existing cash resources, interest income,
external financing from equity offerings, debt financings or collaborative
research and development arrangements with corporate sponsors to finance its
operations.

     Results of operations may vary significantly from period to period
depending on, among other factors, the progress of the Company's research and
development efforts, the receipt, if any, of additional license fees and
milestone payments, the timing of certain expenses, and the establishment of
additional collaborative research agreements.

     The following discussion of the financial condition and results of
operations of the Company should be read in conjunction with the accompanying
consolidated financial statements and the related footnotes thereto.

RESULTS OF OPERATIONS

YEARS ENDED DECEMBER 31, 1998, 1997 AND 1996

     License and research revenues totaled $5,325,000, $5,788,000 and $4,225,000
for the years ended December 31, 1998, 1997 and 1996, respectively.  With the
exception of a $2,000,000 non-refundable upfront payment from Sumitomo
Pharmaceuticals Co., Ltd. relating to the development and commercialization of
the Company's Fabry disease product in Japan and other Asian countries in
1998, all other revenues in each fiscal year were earned from two collaborative
agreements with Hoechst Marion Roussel, Inc. ("HMRI").

     Research and development expenses totaled $25,617,000 in 1998, as compared
to $18,111,000 in 1997 and $14,019,000 in 1996.  The increase in 1998 of
$7,506,000, or 41%, was principally due to increases in external development
services, research and development staffing and laboratory supplies in each of
the Company's product development platforms.  In particular, preclinical and
clinical costs for the Company's Fabry disease and hemophilia A programs, as
well as manufacturing costs associated with the Fabry disease program, were
significant components of the increase.  During 1999, the costs related to both
preclinical and clinical programs are expected to increase significantly as
product development activities are initiated or expanded.  The increase in 1997
of $4,092,000, or 29%, was principally due to an increase in external
development costs,  research and development staffing and laboratory supplies
and expenses related thereto in each of the Company's product development
platforms.

     General and administrative expenses were $6,409,000 for the year ended
December 31, 1998, compared with $6,279,000 and $4,729,000 in 1997 and 1996,
respectively.  The increase in 1998 of


                                         -23-
<PAGE>

$130,000, or 2%,  was principally due to increases in the number of
administrative staff.  The increase in 1997 of $1,550,000, or 33%, was
principally due to increases in administrative employee costs and expenses
associated with being a publicly-held company.  During 1999, general and
administrative costs are expected to increase significantly as the Company
begins to build sales, marketing and distribution capabilities related to the
commercialization of products in its Niche Protein product platform.

     Interest income was $6,736,000, $5,731,000 and $2,551,000 for the years
ended December 31, 1998, 1997 and 1996, respectively.  The average cash and
marketable securities balances were $120,779,000, $102,161,000 and $48,673,000
in 1998, 1997 and 1996, respectively.  The increases in interest income in 1998
and 1997 resulted generally from higher average balances in each of the years.
Higher average balances in the respective years resulted from the Company's
initial public offering in October 1996 and a follow-on offering in July 1997.
In 1998, the effect of the increase in average balances on interest income was
offset by a decline in yield.  In the current interest rate environment, the
Company anticipates yields from cash and marketable securities will decline
significantly from amounts earned in 1998 and 1997.

     The Company had a net loss of $19,965,000, $12,871,000 and $11,972,000 in
1998, 1997 and 1996, respectively.


LIQUIDITY AND SOURCES OF CAPITAL

     Since its inception, the Company has financed its operations through the
sale of Common and Preferred Stock, borrowings under debt agreements, revenues
from collaborative agreements and interest income.

     The Company had unrestricted cash, cash equivalents and marketable
securities totaling $110,155,000 at December 31, 1998.  Cash equivalents and
marketable securities are invested in U.S. Treasury notes, agencies of the U.S.
government and money market funds.

     In July 1997, the Company completed a direct placement of 1,700,000 shares
of common stock, resulting in net proceeds to the Company of $52,900,000.

     The Company leased additional facilities in the fourth quarter of 1998
which will be used for research and development.  Equipment and improvements to
the space are estimated to cost approximately $14,000,000.  In December 1998,
the Company obtained an unsecured term loan facility for up to $14,000,000 to
finance the capital costs related to the leased space.  The loan is payable
beginning in December 1999 on the basis of a seven year amortization schedule
over a five year period, with a final payment for any remaining amount in
September 2004.  The note contains certain restrictive covenants, including,
among other things, minimum cash and tangible net asset requirements and
limitations on the payment of dividends.  At December 31, 1998, no amounts were
outstanding under this facility.

     Even after lease of the new space referred to in the prior paragraph, the
Company's facilities  may not be adequate to accommodate the Company's needs
beyond 2000.  The Company currently expects to meet any additional facilities
requirements through development of a new facility or conversion of an existing
building.  The Company intends to seek financing for all or a significant
portion of the cost of any additional facilities.  There can be no guarantee
that financing will be available on favorable terms, if at all.


                                         -24-
<PAGE>

     At December 31 1998, the Company had commitments totaling $6,911,000 for
certain product development activities with third parties for 1999.

     In May 1994, the Company and HMRI entered into an agreement to
commercialize the Company's GA-EPO product.  Under the terms of the agreement,
HMRI is obligated to pay the Company a total of $58,000,000 upon completion of
all milestones and objectives set forth in the agreement.  As of December 31,
1998, the Company had received $26,500,000.  The remaining $31,500,000 in
payments are contingent upon HMRI's achievement of certain GA-EPO clinical
development milestones.

     In March 1995, the Company entered into a second agreement with HMRI to
commercialize GA-II.  Pursuant to the agreement, the Company also granted HMRI
an option to commercialize certain aspects of the Company's gene therapy
technologies applicable to this protein.  Under the terms of the agreement, HMRI
is obligated to pay the Company a total of $67,000,000 upon completion of all
milestones and objectives set forth in the agreement.  At December 31, 1998, the
Company had received $30,500,000.  The remaining $36,500,000 to be paid to the
Company by HMRI consists primarily of milestone payments contingent upon the
development of the product resulting from the licensed technology.

     HMRI is responsible for the worldwide development, manufacturing and
marketing of GA-EPO, and the Company is entitled to receive a royalty based on
net sales.

     At December 31, 1998, the Company had net operating loss carryforwards of
approximately $62,700,000, which expire at various times through 2013.  Due to
the degree of uncertainty related to the ultimate use of loss carryforwards and
tax credits, the Company has fully reserved against any potential tax benefit.
The future utilization of net operating loss carryforwards and tax credits may
be subject to limitation under the changes in stock ownership rules of the
Internal Revenue Code.  Because of this limitation, it is possible that taxable
income in future years, which would otherwise be offset by net operating losses,
will not be offset and, therefore, will be subject to tax.

     Substantial additional funds will be required to support the Company's
research and development programs, for acquisition of technologies, for
preclinical and clinical testing of its products, pursuit of regulatory
approvals, acquisition of capital equipment, expansion of laboratory and office
facilities, establishment of production capabilities, establishment of sales,
marketing and distribution capabilities and for general and administrative
expenses.  Until such time, if any, as the Company's operations generate
significant revenues from product sales, cash resources, interest income and
proceeds from equity offerings, debt financings and funding from collaborative
arrangements will be required to fund operations.

     The Company expects to pursue opportunities to obtain additional financing
in the future through equity financings, debt financings, lease arrangements
related to facilities and capital equipment and collaborative research
agreements.  The source, timing and availability of any future financing will
depend principally upon equity and debt market conditions, interest rates and,
more specifically, on the Company's continued progress in its exploratory,
preclinical and clinical development programs.  There can be no assurance that
such funds will be available on favorable terms, if at all.

     The Company expects that its existing capital resources, together with
revenues from collaborative agreements and interest income, will be sufficient
to fund its operations into 2001.  The Company's cash requirements may vary,
however, depending on numerous factors.  Lack of necessary funds may require the
Company to delay, scale back or eliminate some or all of its research and
product development programs or to license its potential products or
technologies to third parties.


                                         -25-
<PAGE>

     The Company has been engaged in litigation with Amgen Inc. with respect to
the development of GA-EPO.  See Note 11 to Notes to Consolidated Financial
Statements, which is incorporated by reference herein.

YEAR 2000

     The Year 2000 issue results from computer programs and systems that were
created to accept only two digit dates.  As a result, some computer programs are
unable to differentiate between the year 1900 and the year 2000.  This could
result in miscalculations and system failures.

     The Company has established a multidisciplinary Year 2000 project
committee.  The committee has assessed the Company's software, hardware,
communications systems, applications and networks, as well as other date
sensitive equipment.  Mission critical systems such as the accounting system
have been found compliant or will be upgraded prior to June 1999.  The remaining
systems are currently being tested to identify those systems which would be
affected by Year 2000 non-compliance.  In most cases, vendors have offered free
upgrades or the systems were already scheduled for upgrade.   Therefore, the
cost for obtaining Year 2000 compliance will be minimal for internal systems.
The Company believes its internal systems will not pose significant operating
issues for the Company as a result of the Year 2000.

     In addition to the Company's internal risks, the Company is dependent upon
a number of third parties that provide information, goods and services to the
Company.  These include financial institutions, suppliers, service providers,
public utilities and research partners.  If these third parties experience
failures in their computer systems or equipment due to Year 2000 non-compliance,
it could seriously affect the Company's business operations.  The Company is in
the process  of contacting its significant external business partners to
determine the extent to which the Company is vulnerable to their failure.  The
Company expects this process to be complete by September 1999.

     If third party providers are not able to supply the Company, the Company
could experience delays in its research and development including delays in
clinical trial development or the submission of products for regulatory
approval.  As a contingency plan, the Company expects to identify, if available,
a secondary source for critical third party providers. The Company has not yet
incurred significant cost to address the Year 2000 issue.  While the total cost
of obtaining Year 2000 compliance is not known at this time, the Company
believes the cost will not be material.


FORWARD LOOKING STATEMENTS

     Statements that are not historical facts, including statements about the
Company's confidence and strategies and its expectations about future products,
technologies and opportunities, market demand or acceptance of future products
are forward-looking statements.  Without limiting the foregoing, the words
"believes", "anticipates", "plans", "expects", "intends" and similar expressions
are intended to identify forward-looking statements.  There are a number of
important factors that could cause the Company's actual results to differ
materially from those indicated by such forward-looking statements, including,
without limitation, whether any of the Company's Gene Activated, gene therapy,
or Niche Protein product candidates will advance in the clinical trial process,
the timing of such clinical trials, whether the clinical trial results will
warrant continued product development, the timing of making required regulatory
filings such as Investigational New Drug applications, and other risks set forth
below, under the caption "Certain Factors That May Affect Future Results."


                                         -26-
<PAGE>

CERTAIN FACTORS THAT MAY AFFECT FUTURE RESULTS

     The following important factors, among others, could cause actual results
to differ from those indicated by forward-looking statements made in this Annual
Report on Form 10-K for the year ended December 31, 1998 and presented elsewhere
by management from time to time.

     PATENT LITIGATION.   The biotechnology industry has been characterized by
significant litigation and interference proceedings regarding patents, patent
applications and other intellectual property rights, and many companies in the
biotechnology industry have attempted to employ intellectual property litigation
to gain or preserve a competitive advantage.  For example, there has been
substantial intellectual property litigation between suppliers of erythropoietin
throughout the world.

     In April 1997, Amgen Inc. filed a civil action in the U.S. District Court
in Massachusetts against the Company and Hoechst Marion Roussel, Inc. ("HMRI"),
the Company's collaborative partner.  The complaint in the action alleged that
the Company's Gene Activated product development program for the production of
GA-EPO and processes for producing GA-EPO infringe on Amgen's U.S. Patent
Numbers 5,547,933, 5,618,698, and 5,621,080 and requested that TKT and HMRI be
enjoined from making, using, or selling GA-EPO and that the court award Amgen
monetary damages.

     In November 1997, TKT and HMRI filed a Motion for Summary Judgment.  On the
same date, Amgen filed a Motion for Summary Judgment of Infringement.  TKT and
HMRI opposed that motion, stating that there had been no infringement.

     In April 1998, the U.S. District Court granted TKT and HMRI's Motion for 
Summary Judgment and denied Amgen's Motion for Summary Judgment on the ground 
that all of TKT and HMRI's GA-EPO related activities to that date had been 
solely for uses reasonably related to the production of information for 
submission to the FDA for regulatory approval and, under the Hatch-Waxman Act, 
do not constitute acts of patent infringement.  The Court ordered Amgen's 
remaining claim for declaratory judgment of future infringement 
administratively closed, to be reopened upon motion of either party for good 
cause shown.  The Court also stated that the issuance by the FDA of a product 
license presumably would constitute good cause to reopen that claim.  Finally, 
the Court stated that, should the case be reopened and should Amgen seek 
preliminary equitable relief, the Court will combine the hearing on a 
preliminary injunction with trial on the merits. The Company expects that the 
case will be reopened.

     Should the case be reopened, the Company can provide no assurance as to the
outcome of the litigation.  A decision by the court in Amgen's favor, including
the issuance of an injunction against the making, use or sale of GA-EPO by the
Company and HMRI in the United States, or any other conclusion of such
litigation in a manner adverse to the Company and HMRI, would have a material
adverse effect on the Company's business, financial condition, and results of
operations.

     Pursuant to the Company's license agreement with HMRI, HMRI assumed the
cost of defense of the suit by Amgen.  The Company will reimburse HMRI for the
Company's share of litigation expenses, as defined, from future royalties, if
any, received from the sale of GA-EPO and in certain other circumstances.

     There can be no assurance that the Company will not in the future become
subject, in the United States or any other country, to additional patent
infringement claims, interferences and other litigation involving patents, or
any patents that may issue on any pending patent applications, including Amgen
patent applications.

                                         -27-
<PAGE>

     The defense and prosecution of intellectual property suits and related
legal and administrative proceedings can be both costly and time consuming.
Litigation and interference proceedings could result in substantial expense to
the Company or its corporate partner and significant diversion of effort by the
Company's technical and management personnel.  An adverse determination in
litigation to which the Company may become a party could subject the Company to
significant liabilities to third parties or require the Company to seek licenses
from third parties.  Although a number of patent and intellectual property
disputes in the biotechnology area have been settled through licensing or
similar arrangements, costs associated with any such arrangement may be
substantial and could include ongoing royalties.  Furthermore, there can be no
assurance that necessary licenses would be available to the Company or its
corporate partner or would be available on acceptable terms.  Adverse
determinations in a judicial or administrative proceeding or failure to obtain
necessary licenses could prevent the Company or its corporate partner from
manufacturing and selling some or all of its products, which would have a
material adverse effect on the Company's business, financial condition and
results of operations.

     With respect to gene therapy technology, the Company requested, and the
U.S. Patent and Trademark Office (the "PTO"), declared in January 1996, an
interference regarding a third party's issued patent with broad claims to ex
vivo gene therapy.  The participants in the interference are TKT, Genetic
Therapy, Inc. (a wholly-owned subsidiary of Novartis AG), Syntex (U.S.A.) (a
wholly-owned subsidiary of Roche Holdings, Inc.), and Somatix.  Somatix
subsequently merged into Cell Genesys, Inc. With the possible exception of the
patent involved in the interference, the Company believes its Transkaryotic
Therapy technology does not infringe on patents issued to date.  The PTO
proceeding will determine the patentability of the subject matter of the
interference and which of the parties first developed this subject matter.  The
process to resolve the interference can take many years.  The outcome of
interferences can be quite variable:  for example, none of the four parties may
receive the desired claims, one party may prevail, or a settlement involving two
or more of the parties may be reached.  There can be no assurance that TKT will
prevail in this interference or that, even if it does prevail, that the Company
can meaningfully protect its proprietary position.  In the event TKT does not
prevail in the interference, a January 1997 Federal Trade Commission (the "FTC")
decision may then be relevant.  The FTC entered a consent order to resolve
anticompetitive concerns raised by the merger of Ciba-Geigy Limited and Sandoz
Limited into the newly formed Novartis AG.  As part of the consent order, the
constituent entities of Novartis will be required to provide all gene therapy
researchers and developers with non-exclusive licenses to the patent upon which
Novartis is involved in the interference.  The Company has entered into an
agreement with Somatix under which the Company's ability to market its non-viral
gene therapy products will not be affected should Somatix win the interference.

     Should any of its competitors have filed additional patent applications in
the U.S. that claim technology also invented by the Company, the Company may
have to participate in additional interference proceedings declared by the PTO,
all of which could result in substantial cost to the Company to determine its
rights or potential loss of rights.

     PATENTS AND PROPRIETARY RIGHTS.  The Company's success may depend in large
part on its ability to obtain patent protection for its processes and potential
products in the U.S. and other countries and to obtain the right to use in its
potential products genes or other technology that have been or may be patented
by others.  At December 31, 1998,  the Company had six issued U.S. patents and
28 pending patent applications in the U.S. to protect its proprietary methods
and processes; it has also filed foreign patent applications corresponding to
certain of these U.S. patent applications.  In addition, the Company has entered
into several agreements to license proprietary rights from other parties.
However, the patent situation in the field of biotechnology generally is highly
uncertain and involves complex legal, scientific and factual questions.  To date
there has emerged no consistent policy regarding the breadth of claims allowed
in biotechnology patents.  Accordingly, there can be no


                                         -28-
<PAGE>

assurance that patent applications relating to the technology used by the
Company will result in patents being issued or that, if issued, the patents will
not be challenged, invalidated or circumvented or will afford protection against
competitors with similar technology.

     Many biotechnology and pharmaceutical companies, universities and research
institutions, including competitors with substantial resources, have filed
patent applications and have been issued patents potentially relating to the
Company's technologies.  In addition, certain competitors have filed patent
applications and have been issued patents relating to certain methods of
producing therapeutic proteins that the Company anticipates producing using its
Gene Activation technology.  The Company's technologies and potential products
may be found to conflict or be alleged to conflict with patents which have been
or may be granted to competitors, universities or others.  There are a
substantial number of biotechnology patent applications under review at the PTO.
Because patent applications in the U.S. are maintained in secrecy until patents
issue, the Company cannot be certain that others have not filed or maintained
patent applications for technology used by the Company or covered by the
Company's pending patent applications or that the Company was the first to file
patent applications for such technology.  Competitors may have filed
applications for, or may have received patents and may obtain additional patents
and proprietary rights relating to, compositions of matter or processes that
block or compete with those of the Company.  Furthermore, as is the case with
any pending patent application, competitors may attempt to amend existing
applications to claim rights to compositions of matter or processes that may
block the Company.  No assurance can be given that the Company's products or
processes do not infringe patents that may issue under pending patent
applications.

     Although the Company has licensed proprietary rights to certain genes (for
example, for Factor VIII and Factor IX) to be used in its gene therapy products
and to certain patents (for example, for certain pending and issued patents
related to mucopolysaccharidoses), the Company presently has no proprietary
rights to certain other genes that it may later seek to use in its products and
which may be the subject of issued third party patents or pending patent
applications.  As a result, the Company may be required to obtain licenses under
third party patents in order to market certain of its products.  If such
licenses are not made available to the Company on acceptable terms, the Company
will not be able to market such products.  In addition, under the Company's
license and sublicense agreements, the licensors and sublicensors may terminate
these agreements upon the Company's failure to meet certain specified
milestones.  Any such termination of an existing license or sublicense by any
such licensor or sublicensor, or any inability by the Company to obtain any
required license, could have a material adverse effect on the Company's
business.

     The Company also relies upon unpatented proprietary technology, processes
and know-how, which the Company protects in part by confidentiality agreements
with its employees, consultants and certain contractors.  There can be no
assurance that these agreements will not be breached, that the Company will have
adequate remedies for any breach, or that the Company's trade secrets will not
otherwise become known or be independently developed by competitors.

     EARLY STAGE OF DEVELOPMENT; COMMERCIAL UNCERTAINTY.  TKT is at an early
stage of development.  All of the Company's potential products are in research,
preclinical development or clinical development.  No revenues have been
generated from product sales, and no such revenues are expected until 2000 at
the earliest.

     The Gene Activation products currently under development by the Company
will require significant additional development efforts, including extensive
preclinical and clinical testing and regulatory approval, prior to commercial
use.  There can be no assurance that any Gene Activation products will
ultimately be developed by the Company and its corporate partners, or that, even
if developed, these products will receive regulatory approval.  If approved,
these products may compete


                                         -29-
<PAGE>

with established products of proven safety and efficacy, the manufacturers of
which can be expected to employ intellectual property challenges to
commercialization of these products.  There can be no assurance that the
Company's Gene Activation products, if any, will be able to be commercialized
or, if commercialized, that they will be accepted by medical centers, hospitals,
physicians or patients in lieu of existing treatments.  Accordingly, there can
be no assurance that these products can be successfully manufactured and
marketed at prices that would permit the Company and its corporate partners to
operate profitably.

     The Company's potential gene therapy products may be even further from
commercial introduction.  Due to the early stage of development of the Company's
potential gene therapy products and the extensive research, development,
preclinical and clinical testing, and regulatory review process required before
marketing approval can be obtained, the Company cannot predict with certainty
when it will be able to commercialize any of its potential gene therapy
products, if at all.

     All of TKT's potential Niche Protein products are in research, preclinical
development or clinical development.  No revenues have been generated from
product sales, and the Company believes no such revenues will be realized until
at least 2000.  Extensive research, development, preclinical and clinical
testing and the regulatory review process will be required before marketing
approval can be obtained.  The Company cannot predict with certainty when it
will be able to commercialize any of its potential Niche Protein products, if at
all.

     TECHNOLOGICAL UNCERTAINTY.  Each of the Company's three product platforms
involves new and rapidly evolving technologies.  All of the Company's potential
products are in pre-clinical or clinical stages of development and will require
substantial additional development efforts and regulatory approvals prior to
market introduction.

     The Company's Gene Activated and Niche Protein products are either in
clinical development or have not yet been tested in humans.  While certain of
the Company's potential gene therapy products are in clinical development, the
Company believes that its product candidates in this area are even further from
commercial introduction.  Existing preclinical and clinical data on the safety
and efficacy of the Company's potential products are limited.

     For any given indication, the Company's potential products may not be
efficacious or may prove to have undesirable and unintended side effects,
toxicities or other characteristics that may prevent or limit commercial use.
There can be no assurance that any of the Company's products will obtain
approval from the FDA or equivalent foreign regulatory authorities for any
indication.

     UNCERTAINTY ASSOCIATED WITH CLINICAL TRIALS.  The Company's potential
products are in various stages of research or preclinical or clinical
development. Subject to compliance with FDA regulations, TKT and its corporate
partners plan to undertake extensive clinical testing in humans to evaluate the
safety and efficacy of its products in development.

     The rate of completion of clinical trials is dependent upon, among other
factors, the enrollment of patients.  Patient accrual is a function of many
factors, including the size of the patient population, the proximity of patients
to clinical sites, the eligibility criteria for the study and the existence of
competitive clinical trials.  Delays in planned patient enrollment in the
anticipated Gene Activation clinical trials may result in program delays, which
could have a material adverse effect on TKT.  Even if clinical trials are
completed, there can be no assurance that the Company or its partners will be
able to submit a license application  to the FDA or comparable regulatory
agencies in foreign countries on the schedule anticipated or that such
applications will be reviewed and approved by such regulatory agencies in a
timely manner.


                                         -30-
<PAGE>

     Of the gene therapy products under development at the Company, one, for the
treatment of cachexia, and a second, for the treatment of hemophilia A, are in
Phase I clinical trials. There can be no assurance that the Company will be able
to obtain authorization from the FDA for additional human clinical testing for
any of its other gene therapy products currently in research or preclinical
development.

     There can be no assurance that any authorized clinical testing will be
completed successfully within any specified time period, if at all, with respect
to any potential product.  There also can be no assurance that such testing will
show any potential product to be safe or efficacious or that any such product
will be approved by the FDA for any indication.  Furthermore, the Company or the
FDA may suspend clinical trials at any time if the subjects or patients
participating in such trials are being exposed to unacceptable health risks.
There can be no assurance that the Company will not encounter problems in
clinical trials which will cause the Company or the FDA to delay or suspend
clinical trials.

     UNCERTAINTY OF GOVERNMENT REGULATORY REQUIREMENTS; LENGTHY APPROVAL
PROCESS.  The Company's research and development, preclinical testing, clinical
trials, facilities and manufacturing and marketing of its products will be
subject to extensive regulation by numerous governmental authorities in the U.S.
and other countries.  The regulatory process for new therapeutic products, which
includes preclinical and clinical testing of each product to establish its
safety and efficacy, can take many years and require the expenditure of
substantial resources.  Data obtained from preclinical and clinical activities
are susceptible to varying interpretations which could delay, limit or prevent
FDA regulatory approval.  In addition, delays or rejections may be encountered
based upon changes in FDA policy during the period of product development and
FDA regulatory review of each submitted license application.  Similar delays may
also be encountered and substantial resources expended in foreign countries.

     There can be no assurance that even after such time and expenditures,
regulatory approval will be obtained for any Gene Activated or gene therapy
products developed by the Company.  Moreover, if regulatory approval of a
product is granted, such approval may entail limitations on the indicated uses
for which it may be marketed and contain requirements for post-marketing
follow-up studies.  Because gene therapy is a relatively new technology and
products for gene therapy have not been extensively tested in humans, the
regulatory requirements governing gene therapy products may be subject to
substantial additional review by various regulatory authorities in the U.S. and
abroad.  These requirements may result in extensive delays in initiating
clinical trials of gene therapy products and in the regulatory approval process
in general.

     Any of the foregoing effects of government regulation, as well as of
comparable foreign regulation, could delay the marketing of the Company's
products for a considerable or indefinite period of time, materially increase
the cost involved in developing, manufacturing and marketing the Company's
products, diminish or eliminate any competitive advantage the Company may enjoy,
or otherwise adversely affect the Company's ability to conduct its business.
Compliance with applicable government regulations governing each of the
Company's potential products will require a significant commitment of time,
money and effort by the Company and its corporate partners with no assurances
that any approval will ultimately be granted on a timely basis, if at all.

     HISTORY OF OPERATING LOSSES; FUTURE CAPITAL NEEDS; UNCERTAINTY OF
ADDITIONAL FUNDING.  The Company has experienced significant operating losses
since its inception in 1988.  As of December 31, 1998, the Company had an
accumulated deficit of $69,952,000.  The Company expects that it will continue
to incur substantial losses until at least 2000 and expects cumulative losses to
increase until then as the Company's research and development efforts expand.
The Company expects that such losses will fluctuate from quarter to quarter and
that such fluctuations may be substantial.  There can


                                         -31-
<PAGE>

be no assurance that the Company will ever achieve sales or profitability.  To
date, the Company has not received any revenues from product sales.

     The Company will require substantial funds to conduct research and
development (including preclinical and clinical testing) of its potential
products and to manufacture and market any products that are approved for
commercial sale.  Based on its current operating plan, the Company believes that
its available cash will be adequate to satisfy its capital needs into 2001.  The
Company's future capital requirements will depend on many factors, including
continued progress in its research and development programs, the magnitude of
these programs, the scope and results of clinical trials, the timing and receipt
of milestone payments, the time and costs involved in obtaining regulatory
approvals, the costs involved in preparing, filing, prosecuting, maintaining and
enforcing patent claims and other patent-related costs, competing technological
and market developments, the ability of the Company to establish and maintain
collaborative arrangements, and the cost of manufacturing and commercialization
activities.  The Company also will require capital to fund the costs of its
additional facilities requirements.  The Company intends to seek additional
funding through collaborative arrangements and/or through public or private
financings.  There can be no assurance that additional financing will be
available on acceptable terms, if at all.

     COMPETITION.  The biotechnology industry is characterized by rapid and
significant technological change. There can be no assurance that TKT will
succeed in developing and marketing technologies and products that are more
clinically efficacious and cost-effective than existing established treatments
or new approaches and products developed and marketed by its competitors.  The
development by others of alternative or superior treatment methods could render
the Company's products obsolete or noncompetitive. In addition, treatment
methods not clearly superior to the Company's could achieve greater market
penetration through competitors' superior sales, marketing or distribution
capabilities.

     The Company's products and technologies will be subject to substantial
competition from companies engaged in the commercialization of therapeutic
proteins and gene therapy as well as from companies which have other forms of
treatment for the diseases targeted by the Company.  Many of these competitors
have substantially greater financial and other resources than the Company,
including larger research and development staffs and more experience and
capabilities in conducting research and development activities, testing products
in clinical trials, obtaining regulatory approvals and manufacturing, marketing
and distributing products.  Smaller companies may obtain access to such skills
and resources through collaborative arrangements with pharmaceutical companies
or academic institutions.

     The Company is initially focusing its Gene Activated product efforts on
established products with proven safety and efficacy.  The Company anticipates
that companies selling such products will compete vigorously against any Gene
Activated products offered by the Company or its collaborators.  There can be no
assurance that the Company's Gene Activated products will be accepted by medical
centers, hospitals, physicians or patients in lieu of existing products, or as
to the effect of such competition on the market prices of the Company's
products.

     The Company's Niche Protein products are targeted at patients suffering
from rare genetic diseases.  The Company anticipates that the market for such
products in some instances may be quite small, and that competition in the form
of competitive products could place significant pressure on TKT's ability to
successfully commercialize its products.

     The Company's competitive position also depends on its ability to attract
and retain qualified personnel, obtain patent protection, secure licenses of
necessary genes and technology from third parties, or otherwise develop
proprietary products or processes and secure sufficient capital resources


                                         -32-
<PAGE>

for the typically substantial expenditures and period of time prior to
commercial sales of each product.  There can be no assurance that the Company
will be successful in achieving these goals.

     NO MANUFACTURING OR DISTRIBUTION OR MARKETING CAPABILITIES; DEPENDENCE ON
THIRD PARTY MANUFACTURERS.  Although the Company has pilot gene therapy and
protein manufacturing facilities, it has only limited manufacturing experience
and no commercial scale manufacturing capabilities.  The Company will need to
develop, contract for or otherwise arrange for such capabilities, for example,
through collaborative partners, to commercialize any of its products.  If the
Company is delayed in establishing suitable manufacturing capabilities, the
Company's ability to conduct human clinical testing may be adversely affected,
resulting in the delay of submission of potential products for regulatory
approval and initiation of new development programs.  In addition, there can be
no assurance that the Company will be able to manufacture products at a
reasonable cost, that the Company will be able to price products competitively
or, if priced competitively, that the Company will be able to achieve margins
sufficient to allow it to achieve profitability.

     The Company plans to provide its gene therapy products through central
manufacturing facilities.  The establishment of these facilities will require
substantial additional funds and personnel and will require compliance with
extensive regulations applicable to such facilities.  There can be no assurance
that such funds and personnel will be available on acceptable terms, if at all,
or that the Company will be able to comply with such regulations at acceptable
cost, if at all.  In addition, in managing this expansion the Company may
encounter unforeseen regulatory, logistical or management problems or incur
unexpected operating costs.  Failure or delays in establishing these facilities,
or the incurrence of unexpected operating costs, could adversely affect the
ability of the Company to manufacture and market its gene therapy products.

     To the extent that the Company contracts with third parties for the
manufacture of its products, the Company will be dependent on such third parties
to comply with the terms of the contracts and to manufacture for the Company on
a timely basis and in accordance with applicable regulations. Any failures by
third parties to person their contract obligations satisfactorily may delay
clinical trial development or the submission of products for regulatory
approval, impair the Company's ability to commercialize its products as planned
and deliver products on a timely basis or otherwise adversely affect the
Company's competitive position.

     The Company has no product sales, marketing or distribution capabilities or
experience.   In order to market any of its products, the Company must develop
sales, marketing and distribution  capabilities, either on its own or in
conjunction with others.  There can be no assurance that the Company will be
able to enter into any arrangements for the sale, marketing and distribution of
its products, that such arrangements will be successful or that the Company will
be able to obtain additional capital and expertise to conduct such activities
independently.  In addition, if the Company chooses to conduct such activities
directly, there can be no assurance that the Company will be able to recruit and
maintain a sales force or that a sales force will be able to successfully access
the markets for the Company's products.

     POSSIBILITY OF ORPHAN DRUG STATUS.   The Company believes that many of the
potential products in its Niche Protein platform may qualify as Orphan Drugs.
TKT intends to pursue this designation aggressively, where appropriate, with
respect to its Niche Protein products intended for patient populations in the
United States of less than 200,000.  A drug that receives Orphan Drug
designation by the FDA and is the first product to receive FDA marketing
approval for its stated product claim is entitled to a seven-year exclusive
marketing period in the United States for that product claim.  A drug that is
considered by the FDA to be different than a particular Orphan Drug is not
barred from sale in the United States during such seven-year exclusive marketing
period.  Furthermore, Orphan Drug exclusivity can be terminated for a variety of
reasons, including that the manufacturer of an


                                         -33-
<PAGE>

Orphan Drug cannot provide an adequate supply of the product.  There can be no
assurance that Orphan Drug status will be afforded to any of the Company's
potential products, or, if afforded, that such designations will be maintained.
In addition, the Company could incur substantial costs in asserting any rights
to prevent such uses it may have under the Orphan Drug Act.

     Legislation has in the past been introduced to limit the marketing
exclusivity provided for certain Orphan Drugs.  Although the outcome of that
legislation, if reintroduced, is uncertain, there remains a possibility that
future legislation will limit the incentives currently afforded to the
developers of Orphan Drugs.

     There can be no assurance that other companies will not seek such
designation and obtain FDA marketing approval before the Company obtains such
approval.  If another company obtains Orphan Drug marketing approval and
receives seven-year marketing exclusivity, it is possible that the Company would
not be permitted by the FDA to market a similar product in the United States
during the exclusivity period.

     DEPENDENCE ON KEY PERSONNEL.  The Company's success is highly dependent on
the retention of principal members of its scientific and management staff.
Furthermore, the Company's future growth will require the hiring of significant
numbers of qualified scientific and management personnel.  Accordingly,
recruiting and retaining such personnel in the future will be critical to the
Company's success.  There is intense competition from other companies and
research and academic institutions for qualified personnel in the areas of the
Company's activities, and there can be no assurance that the Company will be
able to continue to attract and retain on acceptable terms the qualified
personnel necessary for the development of its business.

     DEPENDENCE ON COLLABORATIVE PARTNERS.  The Company has entered into
arrangements with HMRI on two of its Gene Activation development programs, with
Sumitomo on one of its Niche Protein products, and with GI on a gene therapy
development program.  Each agreement with HMRI is subject to termination without
cause on short notice under certain circumstances, and there is no assurance
that in the future either partner will not exercise its termination rights.  The
Company is relying on HMRI to develop, conduct clinical trials, obtain
regulatory approval for the sale of, manufacture and market worldwide GA-EPO and
GA-II.  There can be no assurance that these collaborative partners will devote
the resources necessary to complete development of and commercialize these
potential products.  Should these collaborative partners fail to develop and
commercialize these two potential products, the Company's business would be
materially adversely affected.

     The Company's strategy for the research, development and commercialization
of certain of its potential products includes the possibility that it will enter
into various additional arrangements with corporate partners, licensors,
licensees and others.  There can be no assurance that any further arrangements
will be effected in the future.  Although the Company believes parties to any
existing and future arrangements, if entered into, would have economic and other
motivations to perform their contractual responsibilities in full, the amount
and timing of resources which they would devote to these activities would not be
within the control of the Company.  There can be no assurance that such parties
would perform their obligations as expected or that any revenue would be derived
by the Company from such arrangements.

     PRODUCT LIABILITY AND INSURANCE.  The Company's business will in the future
expose it to potential product liability risks which are inherent in the
testing, manufacturing and marketing of human therapeutic products.  Although
the Company has clinical trial liability insurance for trials conducted in the
U.S., the Company does not currently have any product liability insurance, and
there can be no assurance that it will be able to obtain or maintain such
insurance on acceptable terms, if at


                                         -34-
<PAGE>

all, or that any insurance obtained will provide adequate protection against
potential liabilities.  An inability to obtain insurance at acceptable cost or
otherwise protect against potential product liability claims, in addition to
exposing the Company to significant liabilities, could prevent or inhibit the
commercialization of products developed by the Company.

     UNCERTAINTY OF PHARMACEUTICAL PRICING AND REIMBURSEMENT.  The business and
financial condition of pharmaceutical and biotechnology companies will continue
to be affected by the efforts of government and third-party payors to contain or
reduce the cost of health care through various means.  For example, in certain
foreign markets, pricing and profitability of prescription pharmaceuticals is
subject to government control.  In particular, individual pricing negotiations
are often required in each country of the European Community, even if approval
to market the drug is obtained.

     In the U.S. there have been, and the Company expects that there will
continue to be, a number of federal and state proposals to implement similar
government control.  In addition, an increasing emphasis on managed care in the
U.S. has and will continue to increase the pressure on pharmaceutical pricing.
While the Company cannot predict whether any such legislative or regulatory
proposals will be adopted or the effect such proposals or managed care efforts
may have on its business, the announcement of such proposals or efforts could
have a material adverse effect on the Company's ability to raise capital, and
the adoption of such proposals or efforts could have a material adverse effect
on the Company's business, financial condition and results of operations.
Further, to the extent that such proposals or efforts have a material adverse
effect on other pharmaceutical companies that are prospective corporate partners
for the Company, the Company's ability to establish corporate collaborations may
be adversely affected.

     In addition, in both domestic and foreign markets, sales of the Company's
products, if any, will be dependent in part on the availability of reimbursement
from third party payors, such as government and private insurance plans.  Third
party payors are increasingly challenging the prices charged for medical
products and services.  If the Company succeeds in commercializing products,
there can be no assurance that these products will be considered cost effective,
that reimbursement will be available, or if available, that the payor's
reimbursement policies will be adequate to permit the Company to realize a
reasonable return.

ITEM 7A.  QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

     The Company does not believe that there is any material market risk
exposure with respect to derivative or other financial instruments that would
require disclosure under this item.

ITEM 8.   FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA

     The following financial statements and supplementary data are included as
part of this Annual Report on Form 10-K:

     Report of Independent Auditors

     Consolidated Balance Sheets as of December 31, 1998 and 1997

     Consolidated Statements of Operations for the years ended December 31,
     1998, 1997 and 1996

     Consolidated Statement of Stockholders' Equity for the period January 1,
     1996 through December 31, 1998

     Consolidated Statements of Cash Flows for the years ended December 31,
     1998, 1997 and 1996


                                         -35-

<PAGE>

                           REPORT OF INDEPENDENT AUDITORS

Board of Directors and Stockholders
Transkaryotic Therapies, Inc.

We have audited the accompanying consolidated balance sheets of Transkaryotic
Therapies, Inc. (the Company) as of December 31, 1998 and 1997, and the related
consolidated statements of operations, stockholders' equity 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 consolidated financial position of Transkaryotic
Therapies, Inc. at December 31, 1998 and 1997, and the results of its
consolidated operations and its cash flows for each of the three years in the
period ended December 31, 1998, in conformity with generally accepted accounting
principles.



                                                 /s/ Ernst & Young LLP

Boston, Massachusetts
February 5, 1999

                                     -36-
<PAGE>

                           TRANSKARYOTIC THERAPIES, INC.

                            CONSOLIDATED BALANCE SHEETS


<TABLE>
<CAPTION>

 (in thousands, except par values)                           DECEMBER 31,
                                                      -----------------------
                                                        1998          1997
                                                     ----------    ----------
<S>                                                  <C>           <C>
ASSETS
Current assets:
  Cash and cash equivalents                          $   31,760    $   23,922
  Marketable securities                                  78,395       105,632
  Prepaid expenses and other current assets               2,334           551
                                                     ----------    ----------
     Total current assets                               112,489       130,105
Property and equipment, net                               5,140         4,505
Other assets                                                333           338
                                                     ----------    ----------
                                                     $  117,962    $  134,948
                                                     ----------    ----------
                                                     ----------    ----------

LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities:
  Accounts payable                                     $  1,456      $  1,656
  Accrued expenses                                        2,860         1,543
                                                     ----------    ----------
     Total current liabilities                            4,316         3,199

Stockholders' equity:
  Preferred stock, $1.00 par value, 10,000 shares
    authorized; no shares issued and outstanding             --            --
  Common stock, $.01 par value; 30,000 shares
    authorized, 19,126 and 18,929 shares issued
    and outstanding at December 31, 1998 and 1997,
    respectively                                            191           189
  Additional paid-in capital                            186,067       185,451
  Accumulated deficit                                   (69,952)      (49,987)
  Deferred compensation                                  (2,632)       (3,940)
  Accumulated other comprehensive
    income (loss)                                           (28)           36
                                                     ----------    ----------
      Total stockholders' equity                        113,646       131,749
                                                     ----------    ----------
                                                     $  117,962    $  134,948
                                                     ----------    ----------
                                                     ----------    ----------
</TABLE>



            See accompanying Notes to Consolidated Financial Statements.


                                     -37-

<PAGE>

                           TRANSKARYOTIC THERAPIES, INC.

                       CONSOLIDATED STATEMENTS OF OPERATIONS

<TABLE>
<CAPTION>

(in thousands, except for per share amounts)

                                                 YEAR ENDED DECEMBER 31,
                                          -----------------------------------
                                            1998         1997          1996
                                          --------     --------      --------
<S>                                       <C>          <C>           <C>
License and research revenues             $  5,325     $  5,788      $  4,225

Operating expenses:
  Research and development                  25,617       18,111        14,019
  General and administrative                 6,409        6,279         4,729
                                          --------     --------      --------
                                            32,026       24,390        18,748
                                          --------     --------      --------
Loss from operations                       (26,701)     (18,602)      (14,523)
Interest income                              6,736        5,731         2,551
                                          --------     --------      --------

Net loss                                  $(19,965)    $(12,871)     $(11,972)
                                          --------     --------      --------
                                          --------     --------      --------

Basic and diluted net loss per share
  (pro forma in 1996)                     $  (1.05)    $  (0.74)     $  (0.98)
                                          --------     --------      --------
                                          --------     --------      --------

Shares used in computing basic and
  diluted net loss per share (pro forma
   in 1996)                                 19,052       17,394        12,262
                                          --------     --------      --------
                                          --------     --------      --------
</TABLE>



            See accompanying Notes to Consolidated Financial Statements.

                                     -38-

<PAGE>

                            TRANSKARYOTIC THERAPIES, INC.

                  CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY



<TABLE>
<CAPTION>


(in thousands)                                            PREFERRED STOCK                   COMMON STOCK
                                                  ------------------------------    -------------------------------
                                                      SHARES           AMOUNT           SHARES             AMOUNT
                                                  -------------    -------------    -------------     -------------
<S>                                               <C>              <C>              <C>               <C>
BALANCE AT JANUARY 1, 1996                                2,944    $       2,944            5,198     $          52
Issuance of convertible preferred stock                   1,133            1,133               --                --
Issuance of common stock, net                                --               --            2,831                28
Deferred compensation related to restricted
  stock and stock options granted                            --               --               --                --

Compensation expense related to equity issuances             --               --               --                --
Redeemable preferred stock dividend accretion                --               --               --                --
Conversion of preferred stock into common stock          (4,077)          (4,077)           8,585                86
Unrealized loss on marketable securities                     --               --               --                --
Net loss                                                     --               --               --                --
Comprehensive loss                                           --               --               --                --
                                                  -------------    -------------    -------------     -------------
BALANCE AT DECEMBER 31, 1996                                 --               --           16,614               166
Issuance of common stock, net                                --               --            2,315                23
Deferred compensation related to stock options
  granted                                                    --               --               --                --
Reversal of deferred compensation related to
  forfeited restricted stock and stock options
  granted, net                                               --               --               --                --
Compensation expense related to equity issuances             --               --               --                --
Unrealized gain on marketable securities                     --               --               --                --
Net loss                                                     --               --               --                --
Comprehensive loss                                           --               --               --                --
                                                  -------------    -------------    -------------     -------------
BALANCE AT DECEMBER 31, 1997                                 --               --           18,929               189

Issuance of common stock, net                                --               --              201                 2

Compensation expense related to equity issuances             --               --               --               --
  Reversal of deferred compensation related to
  forfeited restricted stock and stock options
  granted, net                                               --               --               (4)               --
Unrealized loss on marketable securities                     --               --               --                --
Net loss                                                     --               --               --                --
Comprehensive loss                                           --               --               --                --
                                                  -------------    -------------    -------------     -------------
BALANCE AT DECEMBER 31, 1998                                 --               --           19,126     $         191
                                                  -------------    -------------    -------------     -------------
                                                  -------------    -------------    -------------     -------------
</TABLE>

          See accompanying Notes to Consolidated Financial Statements

                                     -39-

<PAGE>

<TABLE>
<CAPTION>

                                                                    CUMULATIVE
                                                    ADDITIONAL     ACCRETION OF
(in thousands)                                       PAID-IN         PREFERRED       ACCUMULATED
                                                     CAPITAL           STOCK           DEFICIT
                                                  -------------    -------------    -------------
<S>                                               <C>              <C>              <C>
BALANCE AT JANUARY 1, 1996                        $      58,331    $      (1,440)   $     (25,144)
Issuance of convertible preferred stock                  22,388               --               --
Issuance of common stock, net                            39,032               --               --
Deferred compensation related to restricted
  stock and stock options granted                         5,054               --               --

Compensation expense related to equity issuances             --               --               --
Redeemable preferred stock dividend accretion                --             (158)              --
Conversion of preferred stock into common stock           6,991            1,598               --
Unrealized loss on marketable securities                     --               --               --
Net loss                                                     --               --          (11,972)
Comprehensive loss                                           --               --               --
                                                  -------------    -------------    -------------
BALANCE AT DECEMBER 31, 1996                            131,796               --          (37,116)
Issuance of common stock, net                            53,754               --               --
Deferred compensation related to stock options
  granted                                                   526               --               --
Reversal of deferred compensation related to
  forfeited restricted stock and stock options
  granted, net                                             (625)              --               --
Compensation expense related to equity issuances             --               --               --
Unrealized gain on marketable securities                     --               --               --
Net loss                                                     --               --          (12,871)
Comprehensive loss                                           --               --               --
                                                  -------------    -------------    -------------
BALANCE AT DECEMBER 31, 1997                            185,451               --          (49,987)

Issuance of common stock, net                               808               --               --

Compensation expense related to equity issuances             --               --               --
Reversal of deferred compensation related to
  forfeited restricted stock and stock options
  granted, net                                             (192)              --               --
Unrealized loss on marketable securities                     --               --               --
Net loss                                                     --               --          (19,965)
Comprehensive loss                                           --               --              --
                                                  -------------    -------------    -------------
BALANCE AT DECEMBER 31, 1998                      $     186,067               --    $     (69,952)
                                                  -------------    -------------    -------------
                                                  -------------    -------------    -------------
</TABLE>

          See accompanying Notes to Consolidated Financial Statements

                                     -40-

<PAGE>

<TABLE>
<CAPTION>
                                                                    ACCUMULATED
                                                                       OTHER            TOTAL
(in thousands)                                        DEFERRED     COMPREHENSIVE    STOCKHOLDERS'
                                                   COMPENSATION     INCOME (Loss)      EQUITY
                                                  -------------    -------------    -------------
<S>                                               <C>              <C>              <C>
BALANCE AT JANUARY 1, 1996                              $(1,244)             $42        $  33,541
Issuance of convertible preferred stock                      --               --           23,521
Issuance of common stock, net                                --               --           39,060
Deferred compensation related to restricted
  stock and stock options granted                        (5,054)              --               --

Compensation expense related to equity issuances          1,080               --            1,080
Redeemable preferred stock dividend accretion                --               --             (158)
Conversion of preferred stock into common stock              --               --            4,598
Unrealized loss on marketable securities                     --              (26)             (26)
Net loss                                                     --               --          (11,972)
                                                                                    -------------
Comprehensive loss                                           --               --          (11,998)
                                                  -------------    -------------    -------------
BALANCE AT DECEMBER 31, 1996                             (5,218)              16           89,644
Issuance of common stock, net                                --               --           53,777
Deferred compensation related to stock options granted     (526)              --               --
Reversal of deferred compensation related to
  forfeited restricted stock and stock options
  granted, net                                              625               --               --
Compensation expense related to equity issuances          1,179               --            1,179
Unrealized gain on marketable securities                     --               20               20
Net loss                                                     --               --          (12,871)
                                                                                    -------------
Comprehensive loss                                           --               --          (12,851)
                                                  -------------    -------------    -------------
BALANCE AT DECEMBER 31, 1997                             (3,940)              36          131,749

Issuance of common stock, net                                --               --              810

Compensation expense related to equity issuances          1,116               --            1,116
Reversal of deferred compensation related to
  forfeited restricted stock and stock options
  granted, net                                              192               --               --
Unrealized loss on marketable securities                     --              (64)             (64)
Net loss                                                     --               --          (19,965)
                                                                                    -------------
Comprehensive loss                                           --               --          (20,029)
                                                  -------------    -------------    -------------
BALANCE AT DECEMBER 31, 1998                            $(2,632)            $(28)        $113,646
                                                  -------------    -------------    -------------
                                                  -------------    -------------    -------------

</TABLE>



             See accompanying Notes to Consolidated Financial Statements.


                                     -41-

<PAGE>

                           TRANSKARYOTIC THERAPIES, INC.

                       CONSOLIDATED STATEMENTS OF CASH FLOWS


<TABLE>
<CAPTION>


(in thousands)                                                          YEAR ENDED DECEMBER 31,
                                                         -----------------------------------------------------
                                                              1998                1997                1996
                                                         -------------       -------------       -------------
<S>                                                      <C>                 <C>                 <C>
OPERATING ACTIVITIES:
Net loss                                                 $     (19,965)      $     (12,871)      $     (11,972)
Adjustments to reconcile net loss to net cash
  used for operating activities:
    Depreciation and amortization                                2,056               2,092               1,575
    Compensation expense related to equity
      issuances                                                  1,116               1,179               1,080
Changes in operating assets and liabilities:
    Decrease (increase) in prepaid  expenses and
      other current assets                                      (1,783)                267                (721)
    Increase (decrease) in accounts payable                       (200)              1,044                  97
    Increase in accrued expenses                                 1,317                 801                  21
                                                         -------------       -------------       -------------
Net cash used for operating activities                         (17,459)             (7,488)             (9,920)
                                                         -------------       -------------       -------------

INVESTING ACTIVITIES:
Proceeds from sales of marketable securities                   134,491             117,669              63,871
Purchases of marketable securities                            (107,318)           (147,440)           (116,793)
Purchases of property and equipment                             (2,660)             (2,936)               (779)
Increase in other assets                                           (26)                (74)                (86)
                                                         -------------       -------------       -------------
Net cash provided by (used for) investing activities            24,487             (32,781)            (53,787)
                                                         -------------       -------------       -------------

FINANCING ACTIVITIES:
Issuance of common stock, net                                      810              53,777              39,060
Issuance of convertible preferred stock                             --                  --              23,521
                                                         -------------       -------------       -------------
Net cash provided by financing  activities                         810              53,777              62,581
                                                         -------------       -------------       -------------
Net increase (decrease) in cash and cash equivalents             7,838              13,508              (1,126)
Cash and cash equivalents at January 1                          23,922              10,414              11,540
                                                         -------------       -------------       -------------
Cash and cash equivalents at December 31                 $      31,760       $      23,922       $      10,414
                                                         -------------       -------------       -------------
                                                         -------------       -------------       -------------

</TABLE>




            See accompanying Notes to Consolidated Financial Statements.


                                     -42-

<PAGE>

                           TRANSKARYOTIC THERAPIES, INC.

                     NOTES TO CONSOLIDATED FINANCIAL STATEMENTS



1.  NATURE OF BUSINESS AND BASIS OF PRESENTATION

Transkaryotic Therapies, Inc. ("TKT" or "the Company") is a biopharmaceutical 
company engaged in the development and commercialization of products based on 
its three proprietary development platforms: Gene Activated(TM) proteins, 
Niche Protein(TM) products and gene therapy.

2.  SIGNIFICANT ACCOUNTING POLICIES

PRINCIPLES OF CONSOLIDATION

The consolidated financial statements include the accounts of the Company and
its wholly-owned subsidiary.  All intercompany activity has been eliminated.

USE OF ESTIMATES

The preparation of financial statements in conformity with generally accepted
accounting principles requires management to make estimates and assumptions that
affect the amounts reported in the financial statements and accompanying notes.
Actual results could differ from those estimates.

CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES

Cash equivalents include funds held in investments with original maturities of
three months or less. Marketable securities consist of U.S. government and
agency obligations. The fair values for marketable securities are based on
quoted market prices.

The Company determines the appropriate classification of cash equivalents and
marketable securities at the time of purchase and reevaluates such designation
as of each balance sheet date. The Company has classified such holdings as
available-for-sale securities, which are carried at fair value, with unrealized
gains and losses reported as a separate component of stockholders' equity.

Financial instruments that potentially subject the Company to concentrations of
credit risk consist of temporary cash investments and marketable securities. The
Company maintains cash and cash equivalents with high credit-quality financial
institutions and limits the amount of credit exposure to any one institution.
The Company's credit exposure on its marketable securities is limited by its
diversification among U.S. government and agency obligations.

PROPERTY AND EQUIPMENT

Property and equipment are stated at cost and depreciated using the
straight-line method over estimated useful lives of the respective asset,
ranging from three to five years. Leasehold improvements are stated at cost and
are amortized using the straight-line method over the term of the lease.


                                     -43-

<PAGE>

                           TRANSKARYOTIC THERAPIES, INC.

             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)



STOCK-BASED COMPENSATION

The Company accounts for qualified stock option grants in accordance  with
Accounting Principles Board Opinion No. 25, "Accounting for Stock Issued to
Employees" ("APB 25"), and, accordingly, recognizes no compensation expense for
the issue thereof. For certain non-qualified stock options granted, the Company
recognizes as compensation expense the excess of the deemed fair value of the
common stock issuable upon exercise over the aggregate exercise price of such
options. The compensation is amortized over the vesting period of each option or
the recipient's term of employment, if shorter.  The Company has adopted the
disclosure-only provisions of Statement of Financial Accounting Standard
("SFAS") No. 123, "Accounting for Stock-Based Compensation," and will continue
to account for its stock options plans in accordance with the provisions of APB
25.

LICENSE  AND RESEARCH  REVENUE

Revenues from collaborative agreements are recognized as earned upon either the
execution of the underlying license agreement, the incurrence of reimbursable
expenses or the achievement of certain milestones.

INCOME TAXES

Deferred  tax assets are determined based on differences  between financial
reporting and income tax bases of assets and liabilities, as well as net
operating loss carryforwards, and are measured using the enacted tax rates and
laws that are expected to be in effect  when the differences  reverse. Deferred
tax assets are reduced by a valuation allowance to reflect the uncertainty
associated with their ultimate realization.

NET LOSS PER SHARE

In 1997, the Financial Accounting Standards Board ("the FASB") issued and the
Company adopted SFAS No. 128, "Earnings per Share."  SFAS No. 128 replaced the
calculation of primary and fully diluted earnings per share with basic and
diluted earnings per share.  Unlike primary earnings per share, basic earnings
per share excludes any dilutive effects of options, warrants and convertible
securities.  All loss per share amounts for all periods have been presented and,
where appropriate, restated to conform to SFAS No. 128 and Securities and 
Exchange Commission ("SEC") requirements.

Net loss per share for 1998 and 1997 is computed using the weighted average
number of common shares outstanding.  Pro forma net loss per share for 1996 is
computed using the weighted average number of common shares and convertible
preferred shares outstanding assuming conversion at date of issuance.
Historical loss per share for 1996 has not been presented since such amounts are
not deemed meaningful due to the significant change in the Company's capital
structure that occurred in connection with the Company's initial public offering
in that year.


                                     -44-

<PAGE>

                           TRANSKARYOTIC THERAPIES, INC.

             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

COMPREHENSIVE INCOME

As of January 1, 1998, the Company adopted SFAS No. 130, "Reporting
Comprehensive Income."  SFAS No. 130 establishes rules for the reporting and
display of comprehensive income and its components, including the requirement
that unrealized gains or losses on the Company's available-for-sale securities,
which prior to adoption were reported separately in stockholders' equity, be
included in other comprehensive income.  The adoption of SFAS No. 130 had no
impact on the Company's net loss or stockholders' equity.   Prior year financial
statements have been modified to conform to the requirements of SFAS No. 130.

SEGMENT REPORTING

Effective January 1, 1998, the Company adopted SFAS No. 131 "Disclosures about
Segments of an Enterprise and Related Information."  SFAS No. 131 establishes
standards for the way that public business enterprises report information about
operating segments in annual financial statements and requires that those
enterprises report selected information about operating segments in interim
financial reports.  SFAS No. 131 also establishes standards for related
disclosures about products and services, geographic areas, and major customers.

All of the Company's efforts are devoted to product development platforms that
are managed and reported in one segment: therapeutic products. The Company is
located in the U.S. and derives substantially all of its license and research
revenues from services provided in the U.S. Current licensing agreements provide
for the sale of products in both the U.S. and abroad. To date, the Company has
not recorded revenues from the sale of any product.

3.  MARKETABLE SECURITIES

The following is a summary of available-for-sale securities:

<TABLE>
<CAPTION>

                                   GROSS        GROSS        ESTIMATED
                                 UNREALIZED   UNREALIZED       FAIR
  (in thousands)       COST        GAINS        LOSSES         VALUE
- -----------------   --------     ----------   ----------    ----------
<S>                 <C>          <C>          <C>           <C>
December 31, 1998   $100,768        $100         $(128)      $100,740
                    --------     ----------   ----------    ----------
                    --------     ----------   ----------    ----------

December 31, 1997   $124,795        $ 64         $ (28)      $124,831
                    --------     ----------   ----------    ----------
                    --------     ----------   ----------    ----------
</TABLE>

These securities are classified in the accompanying balance sheet as follows:

<TABLE>
<CAPTION>

(in thousands)                    December 31,
                            ----------------------
                              1998          1997
                            --------      --------
<S>                         <C>           <C>
Cash equivalents            $ 22,345      $ 19,199
Marketable securities         78,395       105,632
                            --------      --------
                            $100,740      $124,831
                            --------      --------
                            --------      --------

</TABLE>


                                     -45-

<PAGE>

                           TRANSKARYOTIC THERAPIES, INC.

             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

Maturities of marketable securities held at December 31, 1998 are as follows:

(in thousands)

<TABLE>

<S>                            <C>
Less than one year             $ 58,562
One through three years          19,833
                               --------
                               $ 78,395
                               --------
                               --------
</TABLE>

4.  PROPERTY AND EQUIPMENT

Property and equipment consists of the following:

<TABLE>
<CAPTION>

 (in thousands)                                           DECEMBER 31,
                                                      --------------------
                                                         1997       1998
                                                      -------      -------
<S>                                                   <C>          <C>
 Leasehold improvements                               $ 6,935      $ 6,083
 Laboratory equipment                                   4,967        4,056
 Office furniture and equipment                         2,320        1,877
 Construction in process                                  435            -
                                                      -------      -------
                                                       14,657       12,016
 Less accumulated depreciation and amortization         9,517        7,511
                                                      -------      -------
                                                      $ 5,140      $ 4,505
                                                      -------      -------
                                                      -------      -------
</TABLE>

Depreciation and amortization expense on property and equipment was $2,025,000,
$1,668,000 and $1,540,000 in 1998, 1997 and 1996, respectively.

5.  ACCRUED EXPENSES

Accrued expenses consist of the following:

<TABLE>
<CAPTION>

(in thousands)                                    DECEMBER 31,
                                              ---------------------
                                               1998          1997
                                              ------        -------
<S>                                           <C>           <C>
External development services                 $1,245        $   157
Salaries and benefits                            530            556
Professional fees                                384            555
Other                                            701            275
                                              ------        -------
                                              $2,860         $1,543
                                              ------        -------
                                              ------        -------
</TABLE>
6.  BANK LOAN

In December 1998, the Company obtained an unsecured term loan facility for up to
$14,000,000 to finance capital equipment and leasehold improvements.  The loan
is repayable beginning in December 1999 on the basis of a seven year
amortization schedule over a five year period, with a final payment for any
remaining outstanding amount in September 2004.  The loan bears interest at
either the prime rate or LIBOR plus 1.50%, at the Company's election. The note
contains certain restrictive covenants including, among other things, minimum
cash and tangible net asset requirements.  As of December 31, 1998, no amounts
were outstanding on the loan.

                                     -46-

<PAGE>

                           TRANSKARYOTIC THERAPIES, INC.

             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

7.  STOCKHOLDERS' EQUITY

COMMON STOCK

In July 1997, the Company completed a directed public offering of 1,700,000
shares of its common stock, resulting in net proceeds to the Company of
approximately $52,900,000.

STOCK COMPENSATION PLANS

The Company has adopted several stock compensation plans, which provide for the
issuance of incentive and nonqualified stock options, stock appreciation rights,
restricted stock, long-term performance awards and stock grants to employees,
Directors and consultants of the Company at prices determined by the Board of
Directors. At December 31, 1998, approximately 2,372,000 shares of common stock
have been reserved for issuance under the plans. Options generally vest ratably
over periods ranging from two to six years and are exercisable for ten years
from the date of grant.

Stock option activity under the plans is as follows:

<TABLE>
<CAPTION>

(in thousands, except share prices)                     1998                        1997                       1996
                                              -----------------------     -----------------------     -----------------------
                                                             Weighted                   Weighted                    Weighted
                                                             Average                     Average                     Average
                                                            Exercise                    Exercise                    Exercise
                                               Shares         Price        Shares         Price        Shares         Price
                                              ---------     ---------     ---------     ---------     ---------     ---------
<S>                                           <C>           <C>           <C>           <C>           <C>           <C>
Outstanding at January 1                            976       $  5.76           906       $  0.36           136       $  0.01
Granted                                             507         25.91           247         21.51           793          0.42
Exercised                                           (51)         1.28           (77)         2.35             -          0.01
Canceled                                            (62)        11.98          (100)         0.56           (23)         0.01
                                              ---------                   ---------                   ---------
Outstanding at December 31                        1,370         12.99           976          5.76          906           0.36
                                              ---------     ---------     ---------     ---------     ---------     ---------
                                              ---------     ---------     ---------     ---------     ---------     ---------
Options exercisable at December 31                  395     $   13.95           137     $    0.67            51     $    0.01
                                              ---------     ---------     ---------     ---------     ---------     ---------
                                              ---------     ---------     ---------     ---------     ---------     ---------
Weighted average fair value per share of
  options granted during the year                           $   25.91                   $   24.24                   $    6.59
                                                            ---------                   ---------                   ---------
                                                            ---------                   ---------                   ---------

</TABLE>

                                     -47-

<PAGE>

The exercise price and life information in regard to significant option groups
outstanding at December 31, 1998 is as follows:



<TABLE>
<CAPTION>

(in thousands, except share prices)


                                                                          EXERCISABLE
                                                                  ----------------------------
                                WEIGHTED
                                 AVERAGE            WEIGHTED
  RANGE OF     NUMBER OF        REMAINING           AVERAGE                        WEIGHTED
  EXERCISE      OPTIONS         CONTRACTUAL         EXERCISE      NUMBER OF        AVERAGE
   PRICES     OUTSTANDING       LIFE (Yrs.)          PRICE         OPTIONS     EXERCISE PRICE
- ------------  -----------       ----------          --------      ----------    --------------
<S>           <C>                <C>                <C>             <C>         <C>
     $.01         662              6.90               $0.01           207             $0.01
$15.00-22.50      377              9.25              $20.03            34            $17.51
$23.13-29.75      101              9.34              $26.73            2             $23.92
$30.50-36.69      198              9.05              $31.89           147            $31.77
$38.50-39.00       32              8.90              $38.57            5             $38.57
                -----                                                 ---
                1,370                                                 395
                -----                                                 ---
                -----                                                 ---
</TABLE>


                                     -48-

<PAGE>

                           TRANSKARYOTIC THERAPIES, INC.

             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

Pursuant to the requirements of SFAS No. 123, the following are the pro forma
net loss and net loss per share for 1998, 1997 and 1996, as if stock-based
compensation had been determined based on the fair value at the grant date for
grants in 1998, 1997 and 1996, consistent with the provisions of SFAS No. 123:

(in thousands, except per share amounts)

<TABLE>
<CAPTION>
                                      1998                              1997                          1996
                          ---------------------------      --------------------------     ---------------------------
                          AS REPORTED      PRO FORMA       AS REPORTED      PRO FORMA     AS REPORTED      PRO FORMA
                          -----------      ---------       -----------      ---------     -----------      ---------
<S>                       <C>              <C>             <C>              <C>           <C>              <C>
Net loss                     $(19,965)      $(23,774)         $(12,871)      $(13,729)       $(11,972)      $(12,783)

Basic and diluted net
loss per share               $  (1.05)      $  (1.25)         $  (0.74)      $  (0.79)       $  (0.98)      $  (1.04)

</TABLE>

The fair value of options issued pursuant to the plans at the date of grant were
estimated using the Minimum Value method for options granted prior to the
initial public offering and the Black-Scholes model for options granted
subsequent to the initial public offering. The estimation of the fair value of
these options at the date of grant used the following assumptions:

<TABLE>
<CAPTION>
                                      1998            1997             1996
                                   ---------         -------        ----------
 <S>                               <C>               <C>            <C>
 Expected life (years)               2.5-7.5         2.5-7.5          2.5-7.5
 Interest rate                     4.48-4.79%         6.5%          5.79-6.30%
 Volatility                           0.70            0.65             0.65
 Forfeiture rate                      10.0%           10.0%            10.0%
</TABLE>

The Company's volatility for the period prior to the initial public offering was
not used in the calculation of the fair value of the options. The Company has
never declared or paid dividends on any of its capital stock and does not expect
to do so in the foreseeable future.

The pro forma effects on 1998, 1997 and 1996 net loss and net loss per share of
expensing the estimated fair value of stock options issued are not necessarily
representative of the effects on reporting the results of operations for future
years as the periods presented include only three years, two years and one year,
respectively, of option grants.

8.  LICENSE AND RESEARCH AGREEMENTS

The Company has license agreements with Hoechst Marion Roussel, Inc. ("HMRI"),
whereby HMRI was granted exclusive rights to make, use and sell worldwide two
therapeutic products produced under patent rights and technologies owned by the
Company. As of December 31, 1998, the Company has received $57,000,000 from the
sale of stock, nonrefundable licensing fees, milestone payments related to the
successful completion of certain development milestones, and contract research
fundings, pursuant to the agreements with HMRI.  As part of these agreements,
HMRI will make additional payments of up to $68,000,000 upon achievement of
certain development milestones and pay royalties based on net sales of the two
products.

For the years ended December 31, 1998, 1997 and 1996, license and research
revenues earned from HMRI totaled $3,325,000, $5,788,000 and $4,225,000,
respectively.  At December 31, 1998, HMRI owned 2,187,000 shares of the
Company's common stock.

For the year ended December 31, 1998, license and research revenues from another
collaborator totaled $2,000,000.

                                     -49-

<PAGE>
                           TRANSKARYOTIC THERAPIES, INC.

             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

The Company licenses certain technology from various universities and research
organizations. Under the terms of these agreements, the Company is required to
make payments of nonrefundable license fees and royalties on future sales of
products employing the technology.

9.  EMPLOYEE RETIREMENT PLAN

The Company maintains a qualified defined contribution plan covering
substantially all employees of the Company. The Company matches 50% of employee
contributions, up to 7% of compensation (5% prior to July 1997). Employer
contributions vest ratably over five years. The related expense was $231,000 ,
$159,000 and $91,000 in 1998, 1997 and 1996, respectively.

10.  INCOME TAXES

At December 31, 1998, the Company had unused net operating loss carryforwards of
$62,700,000 and research and development tax credits of $3,816,000, both of
which expire through 2013.  Due to the degree of uncertainty related to the
ultimate use of the loss carryforwards and tax credits, the Company has fully
reserved this tax benefit.  Additionally, the future utilization of the net
operating loss carryforwards and tax credits may be subject to limitations under
the change in stock ownership rules of the Internal Revenue Service.

Significant components of the Company's deferred tax assets are as follows:

<TABLE>
<CAPTION>

(in thousands)                                December 31
                                         -----------------------
                                           1998           1997
                                         --------        -------
<S>                                      <C>             <C>
Deferred tax assets:
  Net operating loss carryforwards       $ 23,842        $18,370
  Research and development tax credits      3,816          3,050
  Depreciation                              1,525          1,350
  Other                                        57            186
                                         --------        -------
Total deferred tax assets                  29,240         22,956
Valuation allowance                       (29,240)       (22,956)
                                         --------        -------
Net deferred tax assets                  $     --        $    --
                                         --------        -------
                                         --------        -------
</TABLE>

The valuation allowance increased by $6,284,000 and $5,267,000 during 1998 and
1997, respectively, due primarily to the increase in net operating loss
carryforwards and tax credits.

The difference between the Company's "expected" tax benefit, as computed by
applying the U.S. federal corporate tax rate of 34% to the loss before provision
for income taxes and the actual tax is attributable to tax losses and credits
for which the Company has not recognized any tax benefit.

11.  COMMITMENTS AND CONTINGENCIES

In April 1997, Amgen Inc. filed a civil action in the U.S. District Court in
Massachusetts against the Company and HMRI. The complaint in the action alleged
that the Company's Gene Activated erythropoietin product ("GA-EPO") and
processes for producing GA-EPO infringe Amgen's U.S. Patent Numbers 5,547,933,
5,618,698, and 5,621,080 and requested that the Company and HMRI be enjoined
from making, using, or selling GA-EPO and that the court award Amgen monetary
damages.  In November 1997, the Company and HMRI filed a Motion for Summary
Judgment.  On the same date, Amgen filed a Motion for Summary Judgment of
Infringement.  The Company and HMRI opposed that motion, stating that there had
been no infringement.

In April 1998, the U.S. District Court granted the Company and HMRI's Motion for
Summary Judgment and denied Amgen's Motion for Summary Judgment on the ground
that all of the Company and HMRI's GA-EPO

                                     -50-
<PAGE>

                           TRANSKARYOTIC THERAPIES, INC.

             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

related activities to that date had been solely for uses reasonably related to 
the production of information for submission to the U.S. Food and Drug 
Administration (the "FDA") for regulatory approval and, under the Hatch-Waxman 
Act, do not constitute acts of patent infringement.  The Court ordered Amgen's 
remaining claim for declaratory judgment of future infringement administratively
closed, to be reopened upon motion of either party for good cause shown.  The 
Court also stated that issuance by the FDA of a product license presumably 
would constitute good cause to reopen that claim.  Finally, the Court stated 
that, should the case be reopened and should Amgen seek preliminary equitable 
relief, the Court will combine the hearing on a preliminary injunction with 
trial on the merits.  The Company expects that the case will be reopened.

Pursuant to the Amended and Restated License Agreement, dated March 1995, by and
between HMRI and the Company, HMRI has assumed the cost of defense of the suit
by Amgen. The Company will reimburse HMRI for the Company's share of litigation
expenses, as defined, from future royalties, if any, received from the sale of
GA-EPO and in certain other circumstances.  The Company and HMRI believe that
they have substantial defenses to the allegations in the complaint and expect
that their position will be thoroughly vindicated in court.

The Company can provide no assurance as to the outcome of this litigation. A
decision by the court in Amgen's favor, including the issuance of an injunction
against the making, use or sale of GA-EPO by the Company and HMRI in the United
States, or any other conclusion of the litigation in a manner adverse to the
Company and HMRI, would have a material adverse effect on the Company's
business, financial condition, and results of operations.

The Company leases its facilities under operating leases which expire through
2008, subject to renewal provisions.  In addition, the Company has commitments
for certain product development activities with third parties for 1999.  Future
annual minimum payments under such commitments are as follows:


YEAR ENDED
<TABLE>

<S>                  <C>
(in thousands)

  1999               $ 8,758
  2000                 1,595
  2001                 1,605
  2002                 1,504
  2003                 1,484
  Thereafter           1,747
                     -------
                     $16,693
                     -------
                     -------
</TABLE>

Rent expense was $1,316,000, $1,233,000, $1,068,000 in 1998, 1997 and 1996,
respectively.


                                     -51-

<PAGE>

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

                                       None.

                                      PART III

ITEM 10.  DIRECTORS AND EXECUTIVE OFFICERS OF THE REGISTRANT

     The information required by this item is contained in part under the
caption "Executive Officers of the Company" in PART I hereof, and the remainder
is contained in the Company's Proxy Statement for the Company's Annual Meeting
of Stockholders to be held on June 10, 1999 (the "Proxy Statement") under the
caption "Proposal 1 - Election of Directors" and is incorporated herein by this
reference.

ITEM 11.  EXECUTIVE COMPENSATION

     The information required by this item is contained under the caption
"Executive Compensation" in the Company's Proxy Statement and is incorporated
herein by this reference.

ITEM 12.  SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

     The information required by this item is contained in the Company's Proxy
Statement under the caption "Security Ownership of Certain Beneficial Owners and
Management" and is incorporated herein by this reference.

ITEM 13.  CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS

     The information required by this item is contained in the Company's Proxy
Statement under the caption "Certain Transactions" and is incorporated herein by
this reference.

                                       PART IV

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

     (a)  DOCUMENTS FILED AS A PART OF THIS FORM 10-K:

          1.   FINANCIAL STATEMENTS.  The following documents are filed as part
of this Annual Report on Form 10-K:

               Report of Independent Auditors

               Consolidated Balance Sheets as of December 31, 1998 and 1997

               Consolidated Statements of Operations for the years ended
               December 31, 1998, 1997 and 1996

               Consolidated Statement of Stockholders' Equity for the period
               January 1, 1996 through December 31, 1998


                                     -52-

<PAGE>

               Consolidated Statements of Cash Flows for the years ended
               December 31, 1998, 1997 and 1996

               Notes to Consolidated Financial Statements

          2.   FINANCIAL STATEMENT SCHEDULES.  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.   EXHIBITS.  The Exhibits listed in the Exhibit Index immediately
               preceding such Exhibits are filed as part of this Annual Report
               on Form 10-K, and such Exhibit Index is incorporated herein by
               reference.

     (b)  REPORTS ON FORM 8-K:

          No reports on Form 8-K were filed during the quarter ended December
          31, 1998.


                                     -53-
<PAGE>
                                      SIGNATURES

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

                                   TRANSKARYOTIC THERAPIES, INC.


                                   By: /s/ Richard F Selden
                                      -------------------------------
                                           Richard F Selden
                                           President and Chief
                                           Executive Officer
Date:  March 31, 1999

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

           Signature                        Title                     Date

 /s/ Richard F Selden          President, Chief Executive      March 31, 1999
- ---------------------------    Officer and Director
Richard F Selden              (Principal Executive Officer)

 /s/ Daniel E. Geffken         Vice President, Finance and     March 31, 1999
- ---------------------------    Chief Financial Officer
Daniel E. Geffken             (Principal Accounting and
                               Financial Officer)

 /s/ Rodman W. Moorhead, III   Chairman of the Board of        March 31, 1999
- ---------------------------    Directors
Rodman W. Moorhead, III

 /s/ William R. Miller         Director                        March 31, 1999
- ---------------------------
William R. Miller

 /s/ James E. Thomas           Director                        March 31, 1999
- ---------------------------
James E. Thomas

/s/ Peter Wirth                Director                        March 31, 1999
- ---------------------------
Peter Wirth


                                     -54-
<PAGE>


                                   Exhibit Index


 EXHIBIT NO.      DESCRIPTION


 3.1              Amended and Restated Certificate of Incorporation of the
                  Registrant (1)

 3.2              Amended and Restated By-Laws of the Registrant, as
                  amended(2)

 10.1             Stock Purchase Agreement, dated July 1988, by and between
                  Warburg, Pincus Capital Company, L.P. ("Warburg") and the
                  Registrant (3)

 10.2             Amended and Restated Registration Rights Agreement, dated
                  November 3, 1993 and amended on May 13, 1994, March 1, 1995,
                  October 26, 1995, July 10, 1996 and August 7, 1996, by and
                  among the Registrant and certain holders of the Registrant's
                  Preferred Stock named therein (3)

 10.3             Lease Agreement, dated January 1, 1994, by and between the
                  Trust under the Will of Harry F.  Stimpson for office space
                  at 195 Albany Street, Cambridge, Massachusetts (3)

 10.4             Sublease Agreement, dated April 7, 1992, by and between the
                  Massachusetts Institute of Technology and the Registrant,
                  for office space located at 185 Albany Street, Cambridge,
                  Massachusetts (3)

 10.5             1993 Non-Employee Directors' Stock Option Plan (3) (4)

 10.6             1993 Long-Term Incentive Plan (5)

 10.7             Form of Letter Agreement re: Confidentiality, Inventions and
                  Non-Disclosure (3)

 10.8             Form of Letter Agreement re:  Restricted Stock (3)

 10.9             Form of Scientific Advisor Agreement (3)

 10.10            Amended and Restated Promissory Note, dated June 16, 1993,
                  issued by the Registrant to Dr. Richard F Selden, in the
                  original principal amount of $125,000 (3)

 10.11            Amended and Restated Promissory Note, dated April 21, 1995,
                  issued by the Registrant to Dr. Christoph M. Adams, in the
                  original principal amount of $15,000 (3)

 10.12            Amended and Restated Promissory Note, dated May 5, 1995,
                  issued by the Registrant to Dr. Christoph M. Adams, in the
                  original principal amount of $20,000 (3)

 10.13            Employment Agreement, dated June 19, 1991, by and between
                  Dr. Richard F Selden and the Registrant (3) (4)

 10.14            Pledge Agreement, dated May 14, 1991, by and between Dr.
                  Richard F Selden and the Registrant (3)

 10.15            Employment Agreement, dated July 26, 1991, by and between
                  Dr. Douglas A. Treco and the Registrant (3) (4)

                                     -55-
<PAGE>

 10.16            Employment Agreement, dated November 20, 1993, by and
                  between Dr. Christoph M. Adams and the Registrant (3) (4)

 10.17            Pledge Agreement, dated April 21, 1995, by and between Dr.
                  Christoph M. Adams and the Registrant (3)

 10.18            Agreement, dated September 1, 1991, by and between Mr.
                  William R. Miller and the Registrant (3)

 10.19            Agreement, dated July 30, 1993, by and between Warburg and
                  the Registrant (3)

 10.20            Common Stock Purchase Warrant (3)

 10.21            Collaboration and License Agreement, dated July 22, 1993 and
                  amended on May 30, 1996 (3) (6)

 10.22            Amended and Restated License Agreement, dated March 1, 1995,
                  by and between Hoechst Marion Roussel, Inc. ("HMRI") and the
                  Registrant (3) (6)

 10.23            License Agreement, dated March 1, 1995, by and between HMRI
                  and the Registrant (3) (6)

 10.24            Agreement to Nominate, dated September 23, 1996, by and
                  between Warburg and the Registrant (3) (6)

 10.25            Fifth Amendment to Registration Rights Agreement dated
                  October 1, 1996 by and among the Registrant and certain
                  holders of the Registrant's Preferred Stock named therein
                  (3)

 10.26            Employment Agreement dated July 1, 1996 by and between Kurt
                  C. Gunter and the Registrant (4) (7)

 10.27            Consulting Agreement dated November 1, 1996 by and between
                  Peter Wirth and the Registrant (4) (7)

 10.28            Employment Agreement dated February 20, 1997 by and between
                  Daniel E. Geffken and the Registrant (8)

 10.29            Form of Common Stock Purchase Agreement by and between each
                  Purchaser of shares in the Registrant's directed public
                  offering in August 1997 and the Registrant (8)

 10.30            Lease dated November 10, 1998 between 205 Alewife Limited
                  Partnership and the Registrant

 21.1             Subsidiaries of the Registrant

 23.1             Consent of Ernst & Young LLP

 27.1             Financial Data Schedule

- -------------------------------------
(1)  Filed as an exhibit to the Company's Quarterly Report on Form 10-Q for the
     quarter ended September 30, 1996 and incorporated herein by reference.


                                     -56-
<PAGE>

(2)  Filed as an exhibit to the Company's Annual Report on Form 10-K for the
     year ended December 31, 1997 and incorporated herein by reference.

(3)  Filed as an exhibit to the Company's Registration Statement on Form S-1
     (File No.  333-10845) and incorporated herein by reference.

(4)  Management contract or compensation plan or arrangement required to be
     filed as an exhibit pursuant to Item 14(c) of Form 10-K.

(5)  Filed as an exhibit to the Company's Quarterly Report on Form 10-Q for the
     quarter ended March 31, 1998 and incorporated herein by reference.

(6)  Confidential treatment granted as to certain portions.

(7)  Filed as an exhibit to the Company's Annual Report on Form 10-K for the
     year ended December 31, 1996 and incorporated herein by reference.

(8)  Filed as an exhibit to the Company's Registration Statement on Form S-1
     (File No.  333-31957) and incorporated herein by reference.


                                     -57-

<PAGE>

                                                                   Exhibit 10.30

                                                                         11.2.98

                                 LEASE AGREEMENT

      THIS LEASE made and entered into as of this 10 day of November, 1998, by
and between 205 ALEWIFE LIMITED PARTNERSHIP, a Massachusetts limited partnership
("Landlord"), and TRANSKARYOTIC THERAPIES, INC., a Massachusetts corporation
("Tenant").

                              WITNESSETH

      WHEREAS, Landlord is the owner of certain land and a building located at
205 Alewife Brook Parkway, Cambridge, Massachusetts more particularly described
in Exhibit A (the "Premises" or the "Leased Premises"); and

      WHEREAS, Landlord and a related additional party ("Additional Party") are
the owners of certain parking facilities more particularly described in Exhibit
B attached hereto, which parking facilities are included in the Premises demised
hereunder; and

      WHEREAS, Tenant desires to lease from Landlord such land, building and
improvements located thereon, and to lease from Landlord and the Additional
Party the parking facilities more particularly described in Exhibit B, subject
to the terms and conditions hereinafter stated.

      NOW, THEREFORE, in consideration of the mutual covenants herein set forth,
Landlord and Tenant do hereby agree to the terms and conditions set forth in
this Lease.

                                   ARTICLE I.

                                 REFERENCE DATA

      1.1 Definitions. Each reference in this Lease to any of the following
subjects shall be construed to incorporate the date stated for that subject in
this Article.

ANNUAL
FIXED RENT:              From and after the Rent Commencement Date, (a) during
                         the first through the sixth month thereafter,
                         $20,000.00 per month; (b) from and after the seven (7)
                         month following the Rent Commencement Date and through
                         out the Term, $30,115.00 monthly (from and after the
                         second year of the Term, $361,380.00 annually).
<PAGE>

COMMENCEMENT
DATE:                    The date of execution of this Lease.

RENT
COMMENCEMENT
DATE:                    Annual Fixed Rent shall commence on the earlier of (a)
                         the nineth month following the Commencement Date or (b)
                         the date on which Tenant occupies the Premises for the
                         Permitted Uses hereunder and its tenant improvements
                         are completed (provided that such occupancy shall not
                         be deemed to have occurred during the period in which
                         Tenant is installing its improvements, equipment and
                         furnishings in the Premises).

LAND:                    A parcel of land known as 205 Alewife Brook Parkway, 
                         Cambridge, Massachusetts, as more particularly 
                         described in Exhibit A.

LANDLORD'S
ORIGINAL
ADDRESS:                 185 Alewife Brook Parkway, Suite 400
                         Cambridge, MA

LEASE YEAR:              Any period of one year during the Term commencing on 
                         the Commencement Date or on any anniversary thereof.

PERMITTED
USES:                    Any office, laboratory, manufacturing, biotechnology or
                         accessory use permitted under the Cambridge Zoning 
                         By-Law.

PREMISES:                The Land with the building and parking facilities 
                         thereon described in Exhibit A, together with the 
                         parking facilities described in Exhibit B

TENANT'S
ADDRESS:                 195 Albany Street
                         Cambridge, MA 02139

TERM:                    The term of this Lease shall be ten (10) years,
                         commencing on the Commencement Date. Tenant has three
                         (3) additional renewal periods of five (5) years each
                         at Fair Market Rent (see Exhibit C).


                                       -2-
<PAGE>

      1.2 Exhibits: There are incorporated as part of this Lease the following
Exhibits:

                    Exhibit A - Legal Description of the Land
                    Exhibit B - Parking Facilities
                    Exhibit C - Options to Extend
                    Exhibit D - Tenant Improvements
                    Exhibit D-1 Improvements Removable by Tenant

                                   ARTICLE II.

                             PREMISES, TERM AND RENT

      2.1 Demising. Landlord hereby demises and leases to Tenant, and Tenant
hereby hires from Landlord, for the Term, the Premises, as is.

      2.2 Term. Tenant shall have and hold the Premises for a period commencing
on the date of execution of this Lease and continuing for the Term unless sooner
terminated as provided in this Lease.

      2.3 Annual Fixed Rent. Tenant shall pay, without notice or demand, monthly
installments of the Annual Fixed Rent in advance for each full calendar month of
the Term and shall pay in advance the corresponding fraction of said monthly
installment at the beginning or end of the Term in the amounts set forth in
Section 1.1.

      2.4 Immediate Access. From and after the date of execution of this Lease,
Tenant shall be permitted access to the Premises to install the tenant
improvements described in Exhibit D, and its equipment, fixtures, and
furnishings, but such entry by Tenant prior to the Rent Commencement Date shall
be subject to and upon all of the terms, conditions and agreements contained in
this Lease except that Tenant shall not be obligated to pay Annual Fixed Rent.

                                  ARTICLE III.

                                 ADDITIONAL RENT

       3.1 Tax Expenses. During the Term, Tenant shall pay directly to the City
of Cambridge, as Additional Rent, the Tax Expenses (as such term is hereinafter
defined) in accordance with this Section 3.1. The terms used in this Section
3.1. are defined as follows:


                                       -3-
<PAGE>

            (a) "Tax Year" means the 12-month period beginning July 1 of each
year, or if the appropriate governmental tax fiscal period shall begin on any
date other than July 1, such other date.

            (b) "Tax Expenses" with respect to any Tax Year means the aggregate
Real Estate Taxes on the Property with respect to that Tax Year, reduced by any
abatement receipts with respect to that Tax Year.

            (c) "Real Estate Taxes" means all taxes and special assessments of
every kind and nature assessed by any governmental authority on the Premises
which Landlord shall be obligated to pay in connection with the ownership,
leasing or operation of the Premises, and reasonable expenses of any proceedings
for abatement of such taxes including appeals thereof. The amount of special
assessments to be included shall be limited to the amount of the installment
paid in any Tax Year (plus any interest thereon) of such special assessment
which shall be payable over the longest period permitted by law. There shall be
excluded from such taxes all income, estate, succession, inheritance, excess
profit, franchise and transfer taxes.

      Payments by Tenant on account of Tax Expenses shall be made prior to the
date when due. Tenant shall furnish a copy of evidence of such payment to
Landlord upon request therefor. For any tax bill covering a period only
partially occurring during the Term, Tenant shall pay a pro rata portion of the
taxes shown on that bill, which portion shall be based on the number of days in
the tax period for which the bill applies that occur during the term. Landlord
hereby represents and warrants to Tenant that all Tax Expenses in respect of the
Premises have been paid in full through the first and second quarters of fiscal
year 1999, and that the Premises constitute a separate parcel for real estate
tax assessment purposes. If the first and second quarters of fiscal year 1999
have not been paid, or if Landlord fails to timely pay all Tax Expenses for the
Premises through the Commencement Date, Tenant may make payment of the same and
deduct such payments from the Rent payable under this Lease.

      If Landlord elects not to initiate proceedings to contest the amount of
Real Estate Taxes for any Tax Year, Tenant may, at Tenant's expense, bring
appropriate proceedings to contest the amount of the Real Estate Taxes. Landlord
shall cooperate with Tenant in any such proceedings so far as reasonably
necessary. If, as the result of any such contest or review, the Real Estate
Taxes shall be reduced for any Tax Year, the Tax Expenses for that Tax Year
shall be reduced by an amount equal to the reduction in Real Estate Taxes for
such Tax Year less Landlord's reasonable expenses, if any, incurred in
connection with obtaining that reduction. If at the time the Real Estate Taxes
are reduced Tenant has made payments for Tax Expenses in excess of the actual
Tax Expenses due for that Tax Year, the Landlord shall refund such


                                       -4-
<PAGE>

overpayment to Tenant. In the event Tenant initiates abatement proceedings,
Tenant shall make such payments on account of Tax Expenses as may be required by
law.

      3.2 Utilities and Other Services. During the Term, Tenant shall pay
directly to the provider of the service all charges for steam, heat,
air-conditioning, gas, electricity, telephone, janitorial service, fuel, and
trash removal and all other services and utilities furnished directly to the
Premises. Landlord hereby represents and warrants to Tenant that all water,
sewer and other municipal charges in respect of the Premises have been paid in
full through the date of execution of this Lease. If said charges have not been
paid, Tenant may make payment of the same and deduct such payments from the Rent
payable under this Lease. Tenant hereby covenants and agrees that Tenant shall
maintain the exterior of the Premises in good order and condition consistent
with a quality commercial property, including landscaping, exterior cleaning and
snow removal.

      3.3 Net Lease. It is the intent of the parties that the Annual Fixed Rent
be net to the Landlord. Accordingly, Tenant shall pay directly the expenses of
the Leased Premises as defined pursuant to the term of this Lease Agreement
(e.g., taxes, insurance, maintenance and operating expenses) during the term of
this Lease.

                                   ARTICLE IV.

                              TENANT'S ALTERATIONS

      4.1 Except as permitted hereunder, Tenant shall not make alterations and
additions to the Premises except in accordance with plans and specifications
therefor first approved by Landlord, which approval shall not be unreasonably
withheld or delayed and which shall be requested in writing. Landlord shall not
be deemed unreasonable for withholding approval of any alterations or additions
which (a) involve or might adversely affect any structural or exterior element
of the Building, or any area or element outside of the Premises, or (b) will
require unusual expense to re-adapt the Premises to the current use of any
portion of the Premises upon the Lease termination or expiration unless Tenant
first gives assurance acceptable to Landlord that such re-adaptation will be
made prior to such termination or expiration without expense to Landlord.
Notwithstanding the foregoing, the consent of Landlord shall not be required for
(a) the tenant improvements described in Exhibit D, (b) non-structural
alterations, and (c) painting, carpet, and other cosmetic improvements. Except
as set forth in Exhibit D-1 and as may otherwise be agreed by Landlord and
Tenant, all alterations and additions shall become part of the Building and
shall become the property of Landlord upon termination. Tenant shall have no
obligation to remove the tenant improvements described in Exhibit D upon the
expiration of the Term.


                                       -5-
<PAGE>

      4.2 Construction Standard. All construction work permitted or required by
this Lease shall be done in a good and workmanlike manner and in compliance with
all applicable laws and all lawful ordinances, regulations and orders of
Governmental authority and insurers of the Building.

      4.3 Alteration Requirements. Landlord may (but without any implied
obligation to do so) inspect any construction work of Tenant under this Lease at
reasonable times and upon reasonable prior notice to Tenant. Any such entry
shall be subject to Tenant's security precautions for personal safety and the
confidentiality of its business activities. All of Tenant's work shall be
performed by appropriately licensed contractors. Tenant, before its work is
started, shall secure all permits necessary therefor; deliver to Landlord a
statement of the names of all its contractors; and shall cause each contractor
to carry workman's compensation insurance and comprehensive general public
liability insurance in commercially reasonable amounts insuring Landlord and
Tenant as well as the contractors, and deliver to Landlord certificates of all
such insurance. Tenant agrees to pay promptly when due the entire cost of any
work done by Tenant, its agents, employees or independent contractors, and not
to cause or permit any liens for labor or materials performed or furnished in
connection therewith to attach to the Premises and promptly to discharge any
such liens which may so attach.

                                   ARTICLE V.

                CONDITION OF THE PREMISES SURRENDER: HOLDING OVER

      5.1 Maintenance and Repair. Tenant will be responsible to provide that the
Leased Premises shall have adequate electrical, plumbing, heating, ventilation
and air conditioning systems and related fixtures of such systems as herein
provided, which shall be in good order and condition. Tenant will be responsible
for the repairs required to the electrical, plumbing, heating, ventilation, air
conditioning systems and related fixtures of such systems, and for all necessary
maintenance, repairs, alterations and replacements to such systems and related
fixtures, irrespective of the cost thereof. Tenant will also be responsible for
cleaning and maintaining the Leased Premises, including the redecorating of any
interior surfaces and the installation of any replacement floor coverings which
Tenant desires. The structural repairs for which Tenant is responsible include
repairs to the roof of the Building, the slab floor foundation, and utility
systems. Tenant is responsible for the exterior of the building.

      If maintenance or repairs are required to be done or made by Tenant
pursuant to the terms hereof, Landlord may demand that Tenant do or make the
same forthwith, and, if Tenant refuses or neglects or commence such repairs and
complete the same with reasonable dispatch after such demand, Landlord may (but
shall not be required to do so) make or cause such repairs to be made and shall
not be


                                       -6-
<PAGE>

responsible to Tenant for any loss or damage that may accrue to Tenant's
property or business by reason thereof. If Landlord makes or causes such repairs
to be made, Tenant agrees that Tenant will forthwith on demand pay to Landlord
the cost thereof as Additional Rent. In the event that any capital repairs or
replacements to the roof, slab, structure or major base building systems
performed by Tenant hereunder (except for Tenant's initial improvements, as
described in Exhibit D, and except for any capital items unique to Tenant's
research and manufacturing activities, which shall be Tenant's sole
responsibility) have a useful life (determined in accordance with generally
accepted accounting principles on a straight-line basis) which would extend
beyond the Term hereof, Tenant shall be obligated to perform such work only upon
the payment by Landlord to Tenant of the cost of that portion of the work so
allocated to the period beyond the expiration of the Term hereof. For the
purposes of the foregoing sentence only, the Term shall be deemed to include the
initial ten-year term and the three (3) five-year option periods thereafter,
whether or not exercised by Tenant. If Landlord fails to make such payment
within thirty (30) days of written request therefor, Tenant may undertake such
repair or replacement and deduct Landlord's share of the cost thereof from the
payment of Annual Fixed Rent hereunder. Landlord shall have the right to approve
any repair or replacement as to which Landlord is obligated to contribute
hereunder, which approval shall not be unreasonably withheld or delayed.

      5.2 Entry by Landlord. Landlord may enter the Premises for the purpose of
inspecting the same upon reasonable prior notice to Tenant, provided that any
such entry shall be subject to Tenant's security precautions for personal safety
and the confidentiality of its business activities. Landlord shall use
reasonable efforts to minimize interference with Tenant's activities in the
Premises. In no event shall Landlord enter the Premises for the purpose of
marketing the same, nor shall Landlord install any signs for such purpose, until
the last six (6) months of the Term. In case Landlord is prevented or delayed
from performing any covenant, obligation or duty to be performed on Landlord's
part by reason of any external cause, Landlord shall not be liable to Tenant
therefor. If Tenant fails to surrender the Premises to Landlord upon the
expiration of the Term as provided hereunder, Tenant shall be liable to Landlord
for rent at the rate of 150% of the fixed rent payable hereunder until Tenant
vacates the Premises.

      5.3 Surrender. Tenant shall surrender the Premises and all alterations and
additions thereto as hereinabove provided, at the end or earlier termination of
the Term, in the condition described in Section 5.1, first removing all goods
and effects of Tenant and repairing any damage caused by such removal and
restoring the Premises and leaving them clean and neat. Without limiting the
generality of the foregoing, and except as set forth in Exhibit D-1 or as may be
otherwise agreed by Landlord and Tenant, Tenant shall not remove from the
Premises any laboratory fixture, including, without limitation, fixed laboratory
fixtures, laboratory benches, fume hoods, benches and alterations made to bring
the Premises into compliance with the


                                       -7-
<PAGE>

Massachusetts Building Code. Tenant waives all claims against Landlord for any
damage to Tenant resulting from Landlord's retention or disposition of any
alterations or additions or Tenant's personal property remaining on the Premises
on expiration or earlier termination of the Term. Tenant shall be liable to
Landlord for Landlord's cost for storing, removing, and disposing of any
alterations or Tenant's personal property.

      5.4 Holding Over. If Tenant, with Landlord's consent, remains in
possession of the Premises after expiration or earlier termination of the Term,
such possession by the Tenant shall be deemed to be a month-to-month tenancy
terminable on thirty days' notice given at any time by either party. During any
such month-to-month tenancy, Tenant shall pay all rent and other sums required
by this Lease, and all provisions of this Lease except those pertaining to Term
shall apply to the month-to-month tenancy.

                                   ARTICLE VI.

                                TENANT COVENANTS

      Tenant covenants during the Term and for such further time as Tenant
occupies any part of the Premises:

      6.1 Payment of Rent. To pay when due all Annual Fixed Rent and Additional
Rent, all charges for utility services rendered to the Premises, and all other
monies required to be paid by Tenant pursuant to this Lease.

      6.2 Use. Continuously from the Commencement Date to the end of the Term,
to use and occupy the Premises for the Permitted Uses only, and not to use or
devote the Premises or any part thereof for any purpose which is contrary to law
or ordinance or liable to invalidate any insurance on the Building or its
contents.

      Tenant shall comply with all applicable laws, statutes and regulations,
including all environmental laws, Federal and State, including M.G.L. 21E,
applicable to the conduct by Tenant of the Permitted Uses in the Premises, and
shall indemnify and hold harmless Landlord from all claims, loss or damage
arising from any violation thereof by Tenant. Landlord hereby agrees to
indemnify and hold Tenant harmless from any liability arising under all
environmental laws, Federal and State, including M.G.L. 21E, occasioned by the
existing environmental condition of the Premises, except to the extent disclosed
by the environmental report prepared by MacPhail Associates dated November 2,
1998, a copy of which has been provided by Tenant to Landlord (Tenant hereby
acknowledging its acceptance of the matters set forth in said report).


                                       -8-
<PAGE>

      6.3 Compliance with Law. To comply with all federal, state and local laws,
regulations, ordinances, executive orders and similar requirements in effect
from time to time during the Term, including, without limitations, at Tenant's
cost to alter, maintain or restore the Premises to comply with the same, and to
keep the Premises equipped with all safety appliances required by law or
ordinance or any other regulations of any public authority and to procure all
licenses and permits required for the Premises or Tenant's use thereof, it being
understood that any foregoing provisions shall not be construed to broaden in
any way the Permitted Uses. In the event that any capital repairs or
replacements to the Premises required in order to bring the Premises into such
legal compliance (except for Tenant's initial improvements, as described in
Exhibit D, and except for any capital items unique to Tenant's research and
manufacturing activities, which shall be Tenant's sole responsibility) have a
useful life (determined in accordance with generally accepted accounting
principles on a straight-line basis) which would extend beyond the Term hereof,
Tenant shall be obligated to perform such work only upon the payment by Landlord
to Tenant of the cost of that portion of the work so allocated to the period
beyond the expiration of the Term hereof. For the purposes of the foregoing
sentence only, the Term shall be deemed to include the initial ten-year term and
all three (3) five-year option periods thereafter, whether or not exercised by
Tenant. If Landlord fails to make such payment within thirty (30) days of
written request therefor, Tenant may undertake such repair or replacement, and
deduct Landlord's share of the cost thereof from the payment of Annual Fixed
Rent hereunder. Landlord shall have the right to approve any repair or
replacement as to which Landlord is obligated to contribute hereunder, which
approval shall not be unreasonably withheld or delayed.

      6.4 Permitted Entry. To permit Landlord and its agents, after reasonable
notice except in the case of emergencies, to enter the Premises at all
reasonable hours for the purpose of inspecting, testing, or of making repairs to
the same, to show the Premises to prospective purchasers and mortgagees at all
reasonable times, and to show the Premises to prospective tenants during the
last six (6) months of the Term. Any such entry shall be subject to Tenant's
security precautions for personal safety and the confidentiality of its business
activities. Landlord shall use reasonable efforts to minimize interference with
Tenant's activities in the Premises.

      6.5 Overloading. Not to place a load upon any floor in the Premises
exceeding the floor load per square foot of area which such floor was designed
to carry and which is allowed by law.

      6.6 Personal Property Taxes. To pay promptly when due all taxes which may
be imposed upon personal property (including, without limitation, fixtures and
equipment) in the Premises.


                                       -9-
<PAGE>

       6.7 Attorneys' Fees. As Additional Rent, to pay all reasonable costs,
counsel and other fees incurred by Landlord in connection with the successful
enforcement by Landlord of any obligations of Tenant under this Lease.

       6.8 Assignment and Subletting. Except as otherwise provided in this
Section 6.8, not to assign, mortgage, pledge, hypothecate or otherwise transfer
this Lease, or sublet (which term, without limitation, shall include granting of
concessions, licensees and the like) the whole or any part of the Premises
without, in each instance, having first received the consent of Landlord, which
consent shall not be unreasonably withheld, delayed or conditioned. Any
assignment or sublease made without such consent shall be void, and in any case
where Landlord consents to such assignment or subletting, Tenant shall remain
fully and primarily liable for the obligations of the tenant hereunder,
including, without limitation, the obligation to pay Annual Fixed Rent and
Additional Rent as provided under this Lease. In the event that Landlord fails
to respond to Tenant's written request for consent to assign or sublet hereunder
within twenty (20) days, such request shall be deemed given by Landlord and
Tenant may rely thereon.

      Landlord's prior consent shall not be required for an assignment or
sublease to any entity controlling, controlled by, or under common control with
Tenant, or, provided the net worth of the surviving entity is equal to or
greater than the net worth of Tenant on the date of assignment, in connection
with any merger, consolidation or reorganization of Tenant, or sale of all or
substantially all of the assets thereof.

      Tenant shall give Landlord prior notice of any proposed sublease or
assignment as to which consent is required hereunder, specifying the provisions
of the proposed subletting or assignment, including (i) the name and address of
the proposed subtenant or assignee, (ii) a copy of the proposed subtenant's or
assignee's most recent annual financial statement, and (iii) all of the terms
and provisions upon which the proposed subletting or assignment is to be made.

      Except in the case of a sublease or an assignment pursuant to the second
paragraph of this Section 6.8, Tenant shall pay to Landlord as Additional Rent
fifty percent (50%) of any amount Tenant received from any subtenant or assignee
as rent, additional rent or other form of compensation or reimbursement in
excess of the Annual Fixed Rent, Additional Rent and other monies otherwise due
to Landlord pursuant to this Lease (allocable in the case of a sublease to that
portion of the Premises being subleased), following the recovery by Tenant of
(a) any reasonable expenses incurred and paid by Tenant in connection with such
sublease or assignment such as brokerage commissions, fees for legal services,
and expenses of preparing the Premises for occupancy by such subtenant or
assignee, and (b) the unamortized cost of the improvements installed by Tenant
in the Premises for its Permitted Uses.


                                      -10-
<PAGE>

      If this Lease is assigned, or if the Premises or any part thereof is
sublet or occupied by anyone other than Tenant, Landlord may, upon the
occurrence of an event of default thereunder, collect rent and other charges
from the assignee, sublessee or occupant and shall apply the amount collected to
the rent and other charges herein reserved, but no such assignment, subletting,
occupancy or collection shall be deemed a waiver of the prohibitions contained
in this Section 6.8, or the acceptance of the assignee, sublessee or occupant as
a tenant, or a release of Tenant from the further performance by Tenant of
covenants herein contained to be performed by Tenant. The consent by Landlord to
an assignment or subletting shall not be construed to relieve Tenant from
obtaining the express consent in writing of Landlord to any further assignment
or subletting to the extent required hereunder. No assignment, subletting or use
of the Premises by a subsidiary or controlling entity of Tenant or by any other
third party shall affect the Permitted Uses as set forth in Section 1.1 hereof.

                                  ARTICLE VII.

                             INDEMNITY AND INSURANCE

      7.1 Indemnity. To the maximum extent this agreement may be made effective
according to law, each party agrees to defend, save harmless, and indemnify the
other party from any liability or injury, loss, accident or damage to any person
or property, and from any claims actions, proceedings, and expenses and costs in
connection therewith (including without limitation reasonable counsel fees), (i)
arising from the omission, fault, willful act, negligence or other misconduct of
such party, its contractors, agents, employees or invitee, or from any use made
or thing done or occurring on the Premises during the term or during Tenant's
possession of any part of the Premises not due to the omission, fault, willful
act, negligence or other misconduct of the other party, its contractors, agents,
employees or invitees, or failure to perform its obligations hereunder, or (ii)
resulting from the failure of such party to perform and discharge its covenants
and obligations under this Lease, including, without limitation, the violation
of any environmental law or other governmental requirement. This indemnity and
hold harmless agreement shall include indemnity against all costs, expenses and
liabilities incurred in connection with any such claim or proceedings brought
thereon, and the defense thereof.

      7.2 Tenant's Insurance. Tenant agrees to maintain in full force from the
date upon which a Tenant first enters the Premises for any reason, throughout
the Term, and thereafter, so long as Tenant is in occupancy of any part of the
Premises, a policy of comprehensive general liability insurance under which
Landlord and Tenant are named as insureds, and under which the insurer provides
a contractual liability endorsement insuring against all cost, expense and
liability arising out of or based upon any and all claims, accidents, injuries
and damages described in Section 7.1, in


                                      -11-
<PAGE>

the broadest form of such coverage from time to time available. Each such policy
shall be non-cancellable and non-amendable (to the extent that any proposed
amendment reduces the limits or the scope of the insurance required in this
Lease) with respect to Landlord without thirty (30) days prior notice to
Landlord, and a duplicate original thereof shall be delivered to Landlord. As of
the Commencement Date hereof, the minimum limits of liability of such insurance
for each year shall be Three Million Dollars ($3,000,000.00) for combined bodily
injury (or death) and damage to property (per occurrence), and from time to time
during the Term for such higher limits, if any, as are carried customarily in
the Boston/Route 128 area with respect to similar properties.

      At any time when Tenant is performing construction work in or on the
Premises, Tenant shall carry builder's risk insurance satisfactory to Landlord.
Tenant shall provide Landlord with a certificate evidencing such coverage, which
shall state that the coverage cannot be cancelled or amended without thirty
days' prior notice to Landlord.

      Tenant at its cost shall maintain on all its personal property, tenant
improvements and alterations in on or about the Premises a policy of standard
fire and extended coverage insurance, with vandalism and malicious mischief
endorsements, to the extent of their full replacement value. The proceeds for
any such policy shall be used by Tenant for the replacement of personal property
or the restoration of tenant improvements or alterations. Tenant shall deliver a
certificate evidencing such coverage to Landlord, which shall state that the
coverage may not be amended or cancelled without at least thirty days' prior
written notice to Landlord.

      7.3 Tenant's Risk. Tenant agrees that all of the furnishing, fixtures,
equipments, effects, and property of every kind, nature and description of
Tenant, and of all persons claiming by, through or under Tenant which during the
continuance of this Lease or any occupancy of the Premises by Tenant or anyone
claiming under Tenant may be on the Premises, shall be at the sole risk and
hazard of Tenant, and if the whole or any part thereof shall be destroyed or
damaged by fire, water or otherwise, or by the leakage or bursting of pipes or
by theft or from any other cause, no part of said loss or damage is to be
charged to or be borne by Landlord, except that Landlord shall in no event be
exonerated from any liability to Tenant or to any person for any injury, loss,
damage, or liability to the extent such exoneration is prohibited by law and to
the extent otherwise set forth herein.

      7.4 Landlord's Insurance. Landlord shall carry such insurance with respect
to the Premises as may from time to time be deemed reasonably prudent by
Landlord or required by any mortgagee holding a mortgage thereon or any ground
lessor of the Land, which may only include loss of rents coverage if required by
a mortgagee, and in any event shall include all-risk property insurance against
loss by fire and the risks now covered by extended coverage endorsement in an
amount at


                                      -12-
<PAGE>

least equal to 100% of the replacement value of the Building and the
improvements, alterations and additions installed by Tenant therein, exclusive
of foundation, site preparation and other construction costs which would not
need to be duplicated in the event of total destruction of the Building, and
shall supply certificates of all such insurance to Tenant issued by or on behalf
of the insurers named therein by a duly authorized agent. Tenant shall pay
Landlord as Additional Rent the premiums for such insurance within ten (10) days
after Landlord sends Tenant a copy of the invoice for the premium of such
insurance. In the event that Landlord fails to maintain such insurance and to
provide Tenant with evidence of the same within ten (10) days of request
therefor, Tenant may obtain such insurance, and deduct the cost of the same from
the Annual Fixed Rent due hereunder.

      7.5 Subrogation. Any insurance carried by either party with respect to the
Property, or any property therein or occurrences thereon shall, without further
request by either party, if it can be so written without additional premium, or
with an additional premium which the other party elects to pay, include a clause
or endorsement denying to the insurer rights of subrogation against the other
party to the extent rights have been waived by the insured prior to occurrence
of injury or loss. Each party, notwithstanding any provisions of this Lease to
the contrary, hereby waives any rights of recovery against the other for injury
or loss, including, without limitation, injury or loss caused by negligence of
such other party due to hazards covered by insurance containing such clause or
endorsement to the extent of the indemnification received thereunder.

                                  ARTICLE VIII.

                           CASUALTY AND EMINENT DOMAIN

      8.1 Casualty During Term. If, during the Term, the Building shall be
partially damaged (as distinguished from "substantially damaged," as that term
is hereinafter defined) by fire or casualty, Landlord shall proceed promptly to
restore the Building (consistent, however, with governmental laws and codes then
in existence), to substantially the condition thereof at the time of such
damage, but Landlord shall not be responsible for delay in such restoration
which may result from any cause beyond the reasonable control of Landlord.

      If during the Term the Building shall be substantially damaged (as that
term is hereinafter defined) by fire or casualty, the risk of which is covered
by Landlord's insurance, Landlord shall, promptly after such damage and the
determination of the net amount of insurance proceeds available to Landlord,
expend so much as may be necessary of such net amount to restore (consistent,
however, with governmental laws and codes then in existence) the Building to
substantially the condition thereof at the time of such damage. If the Building
shall be substantially damaged by fire or


                                      -13-
<PAGE>

casualty (a) as the result of a risk not covered by the forms of casualty
insurance maintained by Landlord, or (b) the net amount of insurance proceeds
available to Landlord are insufficient to cover the cost of restoring the
Building in the reasonable estimate of Landlord, then in any such case Landlord
may, but shall have no obligation to, restore the Building. If Landlord elects
not to restore the Building, Landlord shall terminate this Lease by giving
notice to Tenant within a reasonable time after Landlord has determined the net
amount of insurance proceeds available to Landlord and the estimated cost of
such restoration.

      If Landlord shall notify Tenant that Landlord does not intend to restore
the Building and intends to terminate the Lease by reason of the unavailability
or insufficiency of insurance proceeds, Tenant shall have the right to
contribute to Landlord the amount of such insufficiency, and if Tenant shall
promptly notify Landlord of Tenant's desire to contribute such insufficiency and
provide Landlord with security for Tenant's undertaking in this respect
satisfactory to Landlord, this Lease shall not terminate and Landlord shall
restore the Building unless otherwise excused and permitted to terminate by some
other provision of this Article VIII.

      Unless Landlord within forty-five (45) days after the casualty advises
Tenant of the status of Landlord's obligations with respect to reconstruction,
Tenant shall have the right to terminate this Lease, such termination to take
effect as of the date of such Tenant's notice. In addition, Tenant shall have
the right to terminate this Lease by written notice to Landlord in the event of
a casualty as to which the restoration period will exceed one hundred fifty
(150) days from the date of the casualty, or in the event that Landlord
commences restoration but fails to complete the same within one hundred fifty
(150) days from the date of the casualty.

      8.2 Casualty at End of Term. If the Premises shall be substantially
damaged by fire or casualty within the last twelve (12) months of the Term (as
the same may have been extended hereunder), either party shall have the right,
by giving notice to the other not later than thirty (30) days after such damage,
to terminate this Lease, whereupon this Lease shall terminate as of the date of
such notice.

      8.3 "Substantially Damaged". The term, "substantially damaged," as used in
this Article VIII, shall refer to damage of such a character that the same
cannot, in ordinary course, reasonably be expected to be repaired within one
hundred twenty (120) days from the time that repair work would commence.

      8.4 Condemnation. Except as hereinafter provided, if the Premises, or such
portion thereof as to render the balance (if reconstructed to the maximum extent
practicable in the circumstances) unsuitable for Tenant's purposes, shall be
taken by eminent domain, Landlord or Tenant shall have the right to terminate
this Lease by notice to the other of its desire to do so, provided that such
notice is given not later than thirty (30) days after the effective date of such
taking. Should any part of the


                                      -14-
<PAGE>

Premises be so taken, and should this Lease be not terminated in accordance with
the foregoing provisions, Landlord agrees to Use due diligence to put what may
remain of the Premises (consistent, however, with governmental laws and codes
then in existence) into proper condition for use and occupation as nearly like
the condition of the Premises prior to such taking as shall be practicable, but
Landlord shall not be required to expend funds in excess of the damages
recovered by Landlord as a result of taking.

      8.5 Abatement of Rent. If the Premises shall be damaged by fire or other
casualty, the Annual Fixed Rent and Additional Rent shall be justly and
equitably abated and reduced according to the nature and extent of the loss of
use thereof suffered by Tenant; and in case of a taking which permanently
reduces the area of the Premises, a just proportion of the Annual Fixed Rent
shall be abated for the remainder of the Term.

      8.6 Condemnation Award. Landlord shall have and hereby reserves and
excepts, and Tenant hereby grants and assigns to Landlord, all rights to recover
for damages to the Premises, and the leasehold interest hereby created, and to
compensation accrued or hereafter to accrue by reason of such taking, damage or
destruction, as aforesaid, and by way of confirming the foregoing, Tenant hereby
grants and assigns to Landlord all rights to such damages or compensation.
Nothing contained herein shall be construed to prevent Tenant from prosecuting
in any condemnation proceedings a claim for recovery of the cost of improvements
installed by Tenant in the Premises, as well as Tenant's fixtures, equipment,
personal property, and relocation expenses.

                                   ARTICLE IX.

                                     DEFAULT

      9.1 Tenant's Default. In the event that:

            (a)   Tenant shall fail to pay the Annual Fixed Rent, Additional
                  Rent or other charges for which provision is made herein on or
                  before the date on which the same become due and payable, and
                  such condition continues for seven (7) days after written
                  notice from Landlord to Tenant that the same are due (but
                  Tenant shall not be entitled to such notice more than twice in
                  any twelve-month period), or

            (b)   Tenant shall fail to perform or observe any other term or
                  condition contained in this Lease and Tenant shall not cure
                  such failure within thirty (30) days after written notice from
                  Landlord


                                      -15-
<PAGE>

                  to Tenant thereof or, if such failure cannot be cured within
                  such thirty (30) days, if Tenant shall fail to commence to
                  cure such failure within such thirty (30) days and promptly
                  and diligently complete the curing of the same, or

            (c)   The estate hereby created shall be taken on execution or by
                  other process of law, or if Tenant shall be judicially
                  declared bankrupt or insolvent according to law, or if any
                  assignment or trust mortgage arrangement, so-called, shall be
                  made of the property of Tenant for the benefit of creditors,
                  or if a receiver, guardian, conservator, trustee in
                  involuntary bankruptcy, or other similar officer shall be
                  appointed to take charge of all or any substantial part of
                  Tenant's property by a court of competent jurisdiction, or if
                  a petition shall be filed for the reorganization of Tenant
                  under any provisions of the Bankruptcy Code now or hereafter
                  enacted and the same is not dismissed within ninety (90) days,
                  or if Tenant shall file a petition for such reorganization, or
                  for arrangements under any provisions of the Bankruptcy Code
                  now or hereafter enacted and providing a plan for a debtor to
                  settle, satisfy or extend the time for payment of debts.

      Then, in any such case, whether or not the Term shall have begun, Landlord
lawfully may, immediately or at any time thereafter, give notice to Tenant
specifying the default and this Lease shall come to an end on the date specified
therein as fully and completely as if such date were the date herein originally
fixed for the expiration of the Term (Tenant hereby waiving any rights of
redemption), and Tenant will then quit and surrender the Premises to Landlord,
but Tenant shall remain liable as hereinafter provided.

      9.2 Damages. In the event that this Lease is terminated under any of the
provisions contained in Section 9.1 or shall be otherwise terminated for breach
of any obligation of Tenant, Tenant covenants to pay to Landlord forthwith on
Landlord's demand, as compensation, an amount equal to the excess, if any, of
the discounted present value of the total rent reserved for the residue of the
Term over the then discounted present fair rental value of the Premises for the
residue of the Term. In calculating the discounted present value, the parties
agree to use a discount rate of two percent (2%) above the prime rate published
by the Wall Street Journal during the twelve (12) months following any such
termination. In calculating the rent reserved, there shall be included, in
addition to the Annual Fixed Rent and all Additional Rent, the value of all
other considerations agreed to be paid or performed by Tenant for said residue
during the twelve months following any such termination. Tenant further
covenants as an additional and cumulative obligation after any such termination
to pay punctually to Landlord during the twelve months following any such
termination all the sums and perform all the obligations which Tenant


                                      -16-
<PAGE>

covenants in this Lease to pay and to perform in the same manner and to the same
extent and at the time as if this Lease had not been terminated. In calculating
the amounts to be paid by Tenant under the next foregoing covenant, Tenant shall
be credited with any amount paid to Landlord pursuant to the first sentence of
this Section 9.2 with the net proceeds of any rent obtained by reletting the
Premises, after deducting all Landlord's expenses in connection with such
reletting, including, without limitation, all repossession costs, brokerage
commission, fees for legal services and expenses of preparing the Premises for
such reletting, it being agreed that Landlord may (i) relet the Premises, or any
part or parts thereof, for a term or terms which may, at Landlord's option, be
equal to or less than or exceed the period which would otherwise have
constituted the balance of the Term, and may grant such concessions and free
rent as Landlord in its reasonable commercial judgment considers advisable or
necessary to relet the same and (ii) make such alterations, repairs and
decorations in the Premises as Landlord in its reasonable commercial judgment
considers advisable or necessary to relet the same, and no action of Landlord is
accordance with the foregoing or failure to relet or to collect rent under
reletting shall operate or be construed to release or reduce Tenant's liability
as aforesaid. Landlord agrees to use reasonable efforts to attempt to relet the
Premises, but shall be entitled to seek to rent other properties of Landlord
prior to reletting the Premises.

      9.3 Remedies Cumulative. The specific remedies to which Landlord may
resort under the terms of this Lease are cumulative and are not intended to be
exclusive of any other remedies or means of redress to which it may be lawfully
entitled in case of any breach or threatened breach by Tenant of any provisions
of this Lease. In addition to the other remedies provide in this Lease, Landlord
shall be entitled to the restraint by injunction of the violation or attempted
or threatened violation of any of the covenants, conditions, or provisions of
this Lease or to a decree completing specific performance of any such covenants,
conditions, or provisions. Nothing contained in this Lease shall limit or
prejudice the right of Landlord to prove for and obtain in proceedings for
bankruptcy, insolvency or like proceedings by reason of the termination of this
Lease, an amount equal to the maximum allowed by any statute or rule of law in
effect at the time when, and governing the proceedings in which, the damages are
to be proved, whether or not the amount be greater, equal to, or less than the
amount of the loss or damages referred to above.

      9.4 Landlord's Election. If Tenant shall at any time default in the
performance of any obligation under this Lease, Landlord shall have the right,
but not the obligation, upon fifteen (15) days' notice to tenant (except in case
of emergency in which case no notice need be given), to perform such obligation
notwithstanding the fact that no specific provisions for such substituted
performance is made in this lease with respect to such default. In performing
such obligation, Landlord may reasonably make any payment of money or perform
any other


                                      -17-
<PAGE>

reasonable act and all sums so paid by Landlord and all necessary incidental
costs and connection with enforcement of its rights under this Section incurred
by Landlord (together with interest at two percent (2%) above the prime rate
from time to time published by the Wall Street Journal) shall be deemed to be
Additional Rent under this Lease and shall be payable to Landlord immediately on
demand. Landlord may exercise its rights under this Section without waiving any
other of its rights or releasing Tenant from any of its obligations under this
Lease.

      9.5 Late Charges. In the event that any payment of Annual Fixed Rent or
Additional Rent shall remain unpaid for a period of seven (7) days after written
notice from Landlord to Tenant, there shall become due to Landlord from Tenant,
as Additional Rent and as compensation for Landlord's extra administrative costs
in investigating the circumstances of late rent, a late charge of three percent
(3%) of the amount overdue.

                                   ARTICLE X.

                     MORTGAGEES' AND GROUND LESSORS' RIGHTS
                              ESTOPPEL CERTIFICATE

      10.1 Subordination. Tenant shall, at the request of Landlord, subordinate
this Leave to any and all mortgages or ground leases on the Property, so that
the lien of any such mortgage or ground lease shall be superior to all rights
hereby or hereafter vested in Tenant, on the condition that each such
subordination shall provide by its terms that in the event of foreclosure of
such mortgage or termination of such ground lease, Tenant shall remain
undisturbed in its occupancy of the Premises under the terms and conditions of
this lease, so long as Tenant complies with such terms and conditions. In
addition, and as a condition to the obligations of Tenant hereunder, Landlord
shall deliver to Tenant a Nondisturbance and Attornment Agreement on the
foregoing terms from any existing mortgagee or ground lessee of the Premises,
including any existing mortgagee or ground lessee of the parking facilities
described in Exhibit B. Landlord hereby represents to Tenant that there is no
mortgage presently encumbering the Premises.

      10.2 No Prepaid Rent. No Annual Fixed Rent, Additional Rent, or any other
charge payable to Landlord shall be paid more than thirty (30) days prior to the
due date thereof under the terms of this Lease and payments made in violation of
this provision shall (except to the extent that such payments are actually
received by a mortgagee or ground lessor) be a nullity as against such mortgagee
or ground lessor and Tenant shall be liable for the amount of such payments to
such mortgagee or ground lessor.

      10.3 Opportunity to Cure. No act or failure to act on the part of Landlord
which would entitle Tenant under the terms of this Lease, or by law, to be
relieved of


                                      -18-
<PAGE>

Tenant's obligations to pay Annual Fixed Rent or Additional Rent hereunder or to
terminate this Lease, shall result in a release or termination of such tenant's
obligations or a termination of this Lease unless (a) Tenant shall have first
given written notice of Landlord's act or failure to act to Landlord's
mortgagees of record, if any, of whose identity and address Tenant shall have
been given notice, specifying the act or failure to act on the part of Landlord
which would give basis to Tenant's rights; and (b) such mortgagees, after
receipt of such notice, have failed to or refused to correct or cure the
condition complained of within a reasonable time thereafter, which shall include
a reasonable time for such mortgagee to obtain possession of the Property if
possession is necessary for the mortgagee to correct or cure the condition and
if the mortgagee notifies Tenant of its intention to take possession of the
Property and correct or cure such condition.

      10.4 Estoppel Certificate. Tenant shall from time to time within fifteen
(15) days of a written request by Landlord execute, acknowledge and deliver to
Landlord a statement in writing certifying to Landlord or an independent third
party: that this Lease is unmodified and in full force and effect (or, if there
have been any modifications, that the same is in full force and effect as
modified and stating the modifications); that Tenant has no knowledge of any
defenses, offsets, or counterclaims against its obligations to pay the Annual
Fixed Rent and Additional Rent and to perform its other covenants under this
Lease (or if there are any defenses, offsets, or counterclaims, setting them
forth in reasonable detail); that there are no known uncured defaults of
Landlord or Tenant under this Lease (or if there are known defaults, setting
them forth in reasonable detail); the dates to which the Annual Fixed Rent,
Additional Rent and other charges have been paid; and such other matters as
Landlord may reasonably request. Any such statement delivered pursuant to this
Section may be relied upon by any mortgagee or purchaser of this Premises and
shall be binding on Tenant. Landlord hereby covenants and agrees to furnish
estoppel certificates to Tenant on the same terms and conditions as Tenant is
obligated to furnish the same to Landlord hereunder.

                                   ARTICLE XI.

                                  MISCELLANEOUS

      11.1 No Recordation. Tenant agreed not to record this Lease, but
simultaneous with the execution of this Lease, both parties shall execute and
deliver a memorandum of this Lease in form appropriate for recording or
registration, an instrument acknowledging the Commencement Date of the Term, and
if this Lease is terminated before the Term expires, an instrument in such form
acknowledging the date of termination.


                                      -19-
<PAGE>

      11.2 Notices: Checks. Whenever any notice, approval, consent, request,
election, offer or acceptance is given or made pursuant to this Lease, it shall
be in writing. Communications and payments shall be addressed, if to Landlord,
at Landlord's Original Address or at such other address as may have been
specified by prior notice to Tenant; and if to Tenant, at Tenant's Original
Address, with a copy to Katharine E. Bachman, Esq., Hale and Dorr LLP, 60 State
Street, Boston, Massachusetts 02109, or at such other place as may have been
specified by prior notice to Landlord. Any communication so addressed shall be
deemed duly served on the day delivered, if personally delivered, on the third
business day following the date of mailing if mailed by registered or certified
mail, return receipt requested, or on the day following delivery with a
recognized overnight courier service. If Landlord by notice to Tenant at any
time designates some other person or receive payments or notices, all payments
or notices thereafter by Tenant shall be paid or given to the agent designated
until notice to the contrary is received by Tenant from Landlord. Annual Fixed
Rent and Additional Rent payments required under this Lease shall be deemed
sufficiently paid if made by check collected on first presentation.

      11.3 Successors and Assigns. Subject to Section 6.8 regarding Tenant's
right to assign and sublet, this Lease shall be binding upon and inure to the
benefit of the parties hereto and their respective successors and assigns,
except that the original Landlord named herein and each successive landlord
shall be liable only for obligations accruing during the period of its
ownership.

      11.4 Waiver. The failure of Landlord to Tenant to seek redress for
violation of, or to insist upon strict performance of, any covenant or condition
of this Lease, shall not be deemed a waiver of such violation nor prevent a
subsequent act, which would have originally constituted a violation, from having
all the force and effect of an original violation. The receipt by Landlord of
Annual Fixed Rent or Additional Rent with knowledge of the breach of any
covenant of this Lease shall not be deemed a waiver of such breach. No provision
of this Lease shall be deemed to have been waived by Landlord or Tenant unless
such waiver is in writing and signed by the waiving party. No consent of waiver,
express or implied, by Landlord or by Tenant to or of any breach of any
agreement or duty shall be construed as a waiver or consent to or of any other
breach of the same or any other agreement or duty.

      11.5 Partial Payment. No acceptance by Landlord of a lesser sum than the
Annual Fixed Rent and Additional Rent then due shall be deemed to be other than
a partial installment of such rent due, nor shall any endorsement or statement
on any check or any letter accompanying any check or payment as rent be deemed
an accord and satisfaction, and Landlord may accept such check or payment
without prejudice to Landlord's right to recover the balance of such installment
or pursue any other remedy in this Lease provided the delivery of keys to any
employee of Landlord or


                                      -20-
<PAGE>

to Landlord's agent or any employee thereof shall not operate as a termination
of this Lease or a surrender of the Premises.

      11.6 Severability. If any term of this Lease, or the application thereof
to any person or circumstances, shall to any extent be invalid or unenforceable,
the remainder of this Lease, or the application of such term to persons or
circumstances other than those as to which it is invalid or unenforceable, shall
not be affected thereby, and each term of this Lease shall be valid and
enforceable to the fullest extent permitted by law. The titles of the Articles
are for convenience only and not to be considered in construing this Lease.

      11.7 Quiet Enjoyment. So long as Tenant pays Annual Fixed Rent and
Additional Rent, performs all other Tenant covenants of this Lease and observes
all conditions hereof, Tenant shall peaceably and quietly have, hold and enjoy
the Premises for the Term in accordance with the terms of this Lease.

      11.8 Entire Agreement; Captions. This Lease contains all of the agreements
of the parties with respect to the subject matter thereof and supersedes all
prior dealings between them with respect to such subject matter. The captions of
this Lease shall have no effect on its interpretation.

      11.9 Signs. Tenant at its cost shall have the right to place, construct,
and maintain on the Premises one or more signs advertising its business at the
Premises, and no other signs. Any sign that Tenant has the right to place,
construct, and maintain shall comply with all laws and ordinances, and Tenant
shall obtain any approval required by any such laws and ordinances. Landlord
makes no representation with respect to Tenant's ability to place, construct or
maintain any signs.

      11.10 Parking Lot Use and Maintenance; Cambridge Electric Easement.
Landlord will at all times during the term of this Lease permit free parking by
Tenant, its customers, employees, invitees, agents and caretakers in the parking
areas described in Exhibit B.

      Landlord covenants and agrees to make all payments and perform all
obligations required of Landlord under the Parking Easement from Cambridge
Electric Company referenced in Exhibit B (the "Parking Easement") so that the
same shall remain in full force and effect during the term of this Lease and any
extensions thereof. If Landlord breaches said covenant, Tenant may make payment
or perform such obligations as are required of Landlord under the Parking
Easement and and deduct the cost thereof from the Rent payable under this Lease.
Landlord hereby represents and warrants to Tenant that the Parking Easement is
in full force and effect; that Landlord has made all payments and performed all
obligations of Landlord thereunder through the date hereof; that the rent
payable thereunder for


                                      -21-
<PAGE>

calendar year 1998 was $2,795.00 with respect to Cambridge Electric Company,
which amount has been paid in full; and that Landlord has the right under the
Parking Easement to grant to Tenant the rights with respect thereto granted by
this Lease. Landlord agrees to use best efforts to prevent Cambridge Electric
Company from exercising the right of termination set forth in its Parking
Easement. In the event of termination of the Parking Easement, or in the event
that Tenant is deprived of any of the parking rights referenced in Exhibit B,
Landlord shall use best efforts to provide to Tenant replacement spaces therefor
in a location reasonably convenient to the Premises, including the Fresh Pond
Shopping Center. If Landlord fails to provide replacement spaces upon such
termination, or if such replacement spaces do not conform with the zoning
requirements of the City of Cambridge, then, at Tenant's election, Tenant may
either terminate this Lease upon thirty (30) days prior written notice to
Landlord, or Tenant may make its own arrangements for replacement parking spaces
and deduct the cost thereof from monthly payments of Fixed Rent hereunder.

      11.11 Time of Essence. Time is of the essence of each provisions of this
Lease.

      11.12 Authorization. If either party is a corporation, that party shall
deliver to the other party on execution of this Lease a certified copy of a
resolution of its Board of Directors authorizing the execution of this Lease and
naming the officers that are authorized to execute this Lease on behalf of the
corporation. Each individual executing this Lease warrants and represents that
he or she is duly authorized to execute this Lease on behalf of the party that
he or she represents, and that no further act is required to make this Lease the
binding obligation of such party.

      11.13 Brokerage. Each party represents and warrants to the other party
that the only parties with whom they have dealt who would be entitled to a
brokerage commission in connection with this Lease are Fallon Hines & O'Connor
and Trammel Crow, as to whom Landlord shall be responsible for the payment of
all amounts due. Each party agrees to defend, indemnify, and hold the other
party harmless from any liability arising from a breach of the foregoing
representation and warranty.


                                      -22-
<PAGE>

      Executed as a sealed instrument in two or more counterparts on the day and
year first above written.

                         LANDLORD:         205 Alewife Limited Partnership,
                                           a Massachusetts limited partnership

                                           By:  205 Alewife Corporation,
                                                a Massachusetts corporation,
                                                its general partner


                                               By:  /s/ Nishan Atinizian
                                                    -----------------------
                                                    Nishan Atinizian,
                                                    President


                         TENANT:           Transkaryotic Therapies, Inc.


                                           By: /s/ Daniel E. Geffken
                                               -----------------------
                                           Its: VP, CFO
                                                ---------------------

THE UNDERSIGNED ADDITIONAL PARTY JOINS IN THIS LEASE FOR THE PURPOSES OF
GRANTING TO TENANT THE RIGHT TO PARK IN ITS PARKING FACILITIES LISTED IN EXHIBIT
B DURING THE TERM OF THIS LEASE WITHOUT THE REQUIREMENT OF PAYMENT OF ANY SUMS
IN ADDITION TO THE RENT PAYABLE BY TENANT HEREUNDER, AND WITHOUT THE UNDERSIGNED
INCURRING ANY OTHER LIABILITY OR OBLIGATION UNDER THIS LEASE:


                                           /s/ Rusen Atiniz
                                           --------------------------
                                           Rusen Atiniz, as Trustee of
                                           Fresh Pond Shopping Center Trust
                                           Hereunto duly authorized


                                      -23-
<PAGE>

                                    EXHIBIT A

                             DESCRIPTION OF PREMISES

The land with the building and improvements thereon and appurtenances thereto
located at 205 Alewife Brook Parkway, Cambridge, Massachusetts, more
particularly described in Transfer Certificate of Title No. 205120, filed for
registration with the Middlesex South Registry District of the Land Court in
Registration Book 1155, Page 170.


                                      -25-
<PAGE>

                                    EXHIBIT B

                                     PARKING

      Tenant shall have the exclusive right to the following parking spaces,
which spaces shall be specifically designated by signage prepared by Tenant:

1. Fourteen (14) parking spaces on the Premises at 205 Alewife Brook Parkway.

      Owner: Landlord
      No Mortgagee

2. Twelve (12) parking spaces within the parking easement granted by Cambridge
Electric Company dated October 16, 1987, filed for registration with the
Middlesex South Registry District of the Land Court as Document No. 760840. (the
"Parking Easement").

      Owner: Cambridge Electric Company; Landlord, holder of the
Parking Easement

3. Seventeen (17) parking spaces at the rear of the building on premises at 185
Alewife Brook Parkway, in the location closest to the leased premises

      Owner: Rusen Atiniz, as Trustee of the Fresh Pond Shopping
      Center Trust under declaration of trust dated June 29, 1977,
      recorded with the Middlesex South Registry of Deeds in Book
      13301, Page 110, filed with said Registry District as Document
      No. 561975, as amended of record 
      No Mortgagee 
      Title Reference: Middlesex South Registry of Deeds, Book 28895, Page 398

      All of said parking facilities shall be without additional charge under
this Lease. The foregoing location of all of the foregoing parking spaces are
shown on the attached Exhibit B-1.


                                      -26-
<PAGE>

                                   EXHIBIT B-1

                                [GRAPHIC OMITTED]

                [PLOT PLAN FOR PREMISES; SHOWS PARKING LOCATIONS]
<PAGE>

                                    EXHIBIT C

                                OPTIONS TO EXTEND

      If this Lease is in full force and effect, the Tenant shall have the right
to extend the term of this Lease for three (3) separate five (5) year options of
extension provided written notice of the election of such option shall be
delivered by Tenant to Landlord at least six (6) months prior to the expiration
of the initial term of this Lease, in the case of the first option, and similar
notice prior to the expiration of the first extension for exercise of the second
extension option if applicable and a similar notice prior to the expiration of
the second extension option, if applicable for exercise of the third extension
option. It shall be a condition of the validity of the exercise of such options
that Tenant, at the time required herein for the exercise of said options, and
upon the commencement of the option period, shall not be in default under this
Lease beyond the expiration of any applicable grace period and if at either such
time, the applicable grace period shall not have expired, the condition shall be
determined upon the expiration of the grace period. If said options are duly
exercised, the term of this Lease shall be automatically extended without the
requirement of any further instrument, upon all of the same terms, provisions
and conditions set forth in the Lease, except that the fixed rent for and with
respect to each option term shall be Market Rent determined for each such
period.

      Whenever the term "Market Rent" is required to be determined under this
Lease, the term shall mean the market rate rent chargeable for comparable office
space in the Cambridge, Massachusetts area, assuming the condition of the
Premises as of the date of commencement of the extended term, and shall be
determined as follows:

      (a) By no later than one hundred fifty (150) days preceding the last day
set forth for the Tenant to give notice of its election to extend the term of
this Lease, the Tenant shall send a written request to Landlord requesting
Landlord's determination of the "Market Rent" for the Premises for and with
respect to the five (5) year extension period. Within thirty (30) days after
such request Landlord shall notify Tenant ("Landlord's Notice") of Landlord's
determination of the "Market Rent" for such purpose (the "Determined Market
Rent"). The Tenant's written request to Landlord for a determination of Market
Rent, as set forth above, shall not be deemed to be the Tenant's exercise of its
right to extend the term of this Lease. Tenant shall not be required to exercise
such right to extend until Tenant has received notice of the "Market Rent" as
determined pursuant to this Exhibit C.

      The same procedures shall govern the second five (5) year option if duly
exercised prior to the expiration of the first extended option term and also the
third five (5) year option if duly exercised prior to the expiration of the
second extended option term.


                                      -27-
<PAGE>

      (b) If the Tenant disagrees with the Determined Market Rent as being the
"Market Rent" for the Premises for the extension period, the Tenant shall have
the right to initiate a proceeding hereunder for the determination of such
"Market Rent" by, within ten (10) days after Landlord's Notice, giving written
notice thereof to Landlord which notice shall also appoint a real estate
appraiser who is a designed member in good standing of either the Society of
Real Estate Appraisers or the Appraisal Institute with at least ten (10) years,
full-time commercial appraisal experience for the purpose of establishing such
"Market Rent" by a market survey in the Cambridge, Massachusetts area. Within
ten (10) days after receipt by the Landlord of such notice, the Landlord shall,
by notice to the Tenant, appoint a real estate appraiser, with the same minimum
qualifications set forth in the preceding sentence, to determine jointly with
the Tenant's appraiser such "Market Rent". If within thirty (30) days after the
second appraiser has been appointed, the two designated appraisers are unable to
agree upon such "Market Rent", they shall elect a third appraiser meeting the
qualifications stated in this paragraph within ten (10) days after expiration of
the aforesaid thirty (30) day period. If the two appraisers are not able to
agree upon such third appraiser with the aforesaid ten (10) day period, either
appraiser may request the office of the American Arbitration Association located
nearest to Boston, Massachusetts to designate a third appraiser willing so to
act and an appraiser so appointed shall, for all purposes have the same standing
and powers as though he had been seasonably appointed by the appraisers first
appointed. In the case of the inability or refusal to serve of any person
designated as an appraiser, or in case any appraiser for any reason, ceases to
be such, an appraiser to fill such vacancy, meeting the minimum qualifications
stated above, shall be promptly appointed by Landlord, the Tenant, the appraiser
first appointed by the Tenant, or the said office of the American Arbitration
Association, as the case may be, whichever made the original appointment, or, if
the person who continues to act, or the Landlord or the Tenant may apply to said
office of the American Arbitration Association to fill such vacancy with an
appraiser meeting the minimum qualifications stated above, and any appraiser so
appointed to fill such vacancy shall have the same standing and powers as though
originally appointed. The resulting board of appraisers shall, forthwith upon
their appointment, (i) hear the Parties to this Lease and their witnesses, (ii)
examine the records relating to the Premises, the market surveys and such other
documents and records as may, in their judgment, be necessary, (iii) determine
the "Market Rent" of the Premises for such purposes.

       The costs, other than counsel fees, of such appraisal shall be borne
equally by the Parties. Any determination by a majority of the members of the
board of appraisers shall be final and binding upon the parties, but if a
majority of the members of the board of appraisers are unable to agree upon a
determination, the determination of such third appraiser shall be binding upon
the Parties. Upon determining such Market Rent and after computing the rent as
set forth above, the board of appraisers shall promptly notify the Parties in
writing of such


                                      -28-
<PAGE>

determination. If any party shall fail to appear at the hearings appointed by
the appraisers, the appraisers may act in the absence of such party.

      The determination of the board of appraisers or the third appraiser, as
appropriate, made in accordance with the foregoing provisions shall be final and
binding upon the Parties, such determination may be entered as an award in
arbitration in a court of competent jurisdiction, and judgment thereon may be
entered.

      (c) Upon the determination of such "Market Rent" the Landlord shall use
such in the calculation of the Fixed Rent as set forth in this Lease. If, for
any reason, the decision of the appraiser or the appraisers shall not be
determined before the commencement of the extension period, then the Tenant
shall continue to pay Fixed Rent in monthly installments at the rate in effect
immediately prior to the commencement of such extension period until such
decision of the appraiser(s) shall be made, and upon the decision by the
appraiser(s) an appropriate adjustment shall be made, retroactive to the first
day of such extension, except that Tenant shall not be required to exercise its
right to extend until Tenant has received notice of the "Market Rent" as
determined pursuant to this Exhibit C.


                                      -29-
<PAGE>

                                    EXHIBIT D

                               TENANT IMPROVEMENTS

Tenant improvements are illustrated in drawings prepared by Clifford Hoffman
Associates dated 8/31/98. Tenant improvements shall consist of the complete
interior tenant fitup of 205 Alewife Brook Parkway (29,100 square feet ) will
include the following disciplines, structural, architectural, mechanical and
electrical:

Structural

      o     Remove damaged concrete floor at the rear, right side,
            first floor
      o     Install a series of mini-piles to support new steel columns which
            will extend through the roof at this section. (this steel will be
            used to support new mechanical equipment.)
      o     Reinstall concrete floor at the same elevation as the
            left side floor
      o     Selective demolition of existing non-bearing drywall

Architectural

      o     Erect new walls, ceilings and flooring in accordance with
            architectural floorplans per the following distribution:

<TABLE>
<CAPTION>
       Use                                SF          %
       ---                                --          -

<S>                                       <C>         <C>
       Laboratory                         9,600       32
       Office                             4,600       15
       Storage/warehouse                  2,600       10
       Mechanical                         2,600       10
       Protein Production Suite           9,700       33
</TABLE>

      -     Production suite will be built to clean room standards which meet or
            exceed Class 10,000.
      -     Laboratories shall be typical wet chemistry labs with permanently
            affixed metal casework and epoxy countertops.
      -     An interior elevator will be installed to satisfy ADA
            requirements.

Mechanical

      -     Purchase and install new HVAC equipment including (2) air handlers,
            (2) air-cooled chillers, a gas-fired steam boiler and associated
            ductwork
      -     New high purity utility systems (Clean Steam, RODI, WFI and process
            gases) will be installed.

Electrical

      -     The electrical service will be upgraded at the tenants sole cost
            either through the direct purchase and installation of primary
            switchgear or amortized over a two year period with ComElectric.


                                      -30-
<PAGE>

      All new secondary switchgear gear and power distribution will be installed
along with a natural gas powered standby generator.


                                      -31-
<PAGE>

                                   EXHIBIT D-1

             TENANT IMPROVEMENTS REMOVABLE BY TENANT

      At Tenant's option, the following permanently affixed equipment may be
               removed from the Premises upon lease termination:

      -     Clean steam generator
      -     Reverse osmosis de-ionized (RODI) water generation skid
      -     WFI still
      -     Automated manufacturing equipment
      -     Dedicated process equipment and tanks
      -     Autoclaves
      -     Glasswashers
      -     Biosafety cabinets
      -     Incubators


                                 -32-


<PAGE>


                                                                    Exhibit 21.1

                           Subsidiaries of the Registrant


NAME                               JURISDICTION OF INCORPORATION

TKT Securities Corp.               Massachusetts


<PAGE>
                                                                   Exhibit 23.1


                       Consent of Independent Auditors



We consent to the incorporation by reference in the Registration Statements 
(Form S-8 Nos. 333-19915 and 333-19917) pertaining to the 1993 Long-Term 
Incentive Plan and 1993 Non-Employee Director Stock Option Plan of our report 
dated February 5, 1999, with respect to the consolidated financial statements 
of Transkaryotic Therapies, Inc. included in the Annual Report (Form 10-K) 
for the year ended December 31, 1998.


                                                        /s/ Ernst & Young LLP

Boston, Massachusetts
March 26, 1999


<TABLE> <S> <C>

<PAGE>
<ARTICLE> 5
<MULTIPLIER> 1,000
       
<S>                             <C>
<PERIOD-TYPE>                   YEAR
<FISCAL-YEAR-END>                          DEC-31-1998
<PERIOD-START>                             JAN-01-1998
<PERIOD-END>                               DEC-31-1998
<CASH>                                          31,760
<SECURITIES>                                    78,395
<RECEIVABLES>                                        0
<ALLOWANCES>                                         0
<INVENTORY>                                          0
<CURRENT-ASSETS>                               112,489
<PP&E>                                          14,657
<DEPRECIATION>                                   9,517
<TOTAL-ASSETS>                                 117,962
<CURRENT-LIABILITIES>                            4,316
<BONDS>                                              0
                                0
                                          0
<COMMON>                                           191
<OTHER-SE>                                     113,455
<TOTAL-LIABILITY-AND-EQUITY>                   117,962
<SALES>                                              0
<TOTAL-REVENUES>                                 5,325
<CGS>                                                0
<TOTAL-COSTS>                                   32,026
<OTHER-EXPENSES>                                     0
<LOSS-PROVISION>                                     0
<INTEREST-EXPENSE>                                   0
<INCOME-PRETAX>                               (19,965)
<INCOME-TAX>                                         0
<INCOME-CONTINUING>                           (19,965)
<DISCONTINUED>                                       0
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                  (19,965)
<EPS-PRIMARY>                                   (1.05)
<EPS-DILUTED>                                   (1.05)
        

</TABLE>


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