September 17, 2003

News Release: Tm Bioscience to supply leading reference lab with genetic tests

Tm Bioscience Corporation (TSX Venture: TMC) today announced that Mayo Foundation in Rochester, Minnesota has signed a two-year purchase agreement for the Company's Tag-It(TM) P450-2D6 drug metabolism test. This test will be used by Mayo Medical Laboratories, which provides lab testing and interpretive services for Mayo and for medical centres and hospitals around the world.

'Mayo operates one of the foremost international reference laboratories and is a world-recognized leader in the clinical lab testing industry. We are extremely pleased to have Mayo as a customer for our P450-2D6 drug metabolism test,'said Greg Hines, President and CEO of Tm Bioscience. 'This agreement is also a validation of the effectiveness of Tm's Early Access Program for signing supply agreements with key customers.' The Tag-It(TM) P450-2D6 test was commercially launched by Tm Bioscience in June 2003. Through Tm Bioscience's Early Access Program, Mayo has already started their internal validation process for the test.

The Tag-It(TM) P450-2D6 test will be used to identify the presence or absence of important mutations common in patients with atypical drug metabolism, which can lead to adverse drug responses, a major cause of hospitalization. It is estimated that 20% of currently available prescription drugs are metabolized by P450-2D6 derived enzymes. The demand for genetic tests to identify the presence or absence of important mutations common in patients with atypical drug metabolism is growing rapidly, as drug developers and the medical community face increasing pressure from regulators to characterize patients for improved safety. Hospitalization for adverse drug reactions is the third leading cause of emergency room admissions in the United States.

In addition to Mayo Foundation, Tm Bioscience has a second supply agreement with an unnamed U.S. customer for this product. The Tag-It(TM) P450-2D6 test can also be ordered directly from Tm Bioscience by calling 1 (800) 593-2370.

About Tag-It(TM) genetic tests

Tm Bioscience is commercializing a menu of tests for the rapidly growing genetic testing market. The Company has already commercialized a series of Tag-It(TM) tests for Coagulation Disorders, launched in December 2002, and the first in its series of Drug Metabolism tests, the Tag-It(TM) P450-2D6 test. The Company's pre-commercial pipeline includes the Tag-It(TM) Cystic Fibrosis test, and the Tag-It(TM) P450-2C9 and P450-2C19 Drug Metabolism tests. All of Tm Bioscience's genetic tests are based on the Tm Universal Array platform and operate on the Luminex xMAP system. The Universal Array enables the production of highly accurate, high-throughput, low cost DNA-based tests.

About Tm Bioscience - Putting the Human Genome to Work(TM)

Tm Bioscience is a DNA-based diagnostics company developing a suite of genetic tests. Tm Bioscience's product pipeline includes tests for genetic mutations related to hematology, cystic fibrosis, toxicology and other debilitating genetic disorders. Tm Bioscience is located in Toronto, Ontario. Additional information about Tm Bioscience can be found at www.tmbioscience.com.

The TSX Venture Exchange has not reviewed and does not accept responsibility for the adequacy or accuracy of this release.

SOURCE TM Bioscience

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