Tm BIOSCIENCE ANNOUNCES FIRST SUPPLY AGREEMENT

TORONTO, ON, December 19, 2002 — Tm Bioscience Corporation (TSX Venture: TMC) today announced a development and supply agreement with an undisclosed, U.S. customer for Tm’s Tag-It™ Mutation Detection Kit for P450-2D6. The customer will validate this genetic test. In exchange for early access to the kit, the customer has agreed to purchase a minimum quantity of tests over the next three years. The Tag-It™ Mutation Detection for P450-2D6 is expected to be commercially available in mid-2003. It is estimated that 20% of currently available prescription drugs are metabolized by P450-2D6 derived enzymes.

“We are pleased to sign our first supply agreement with a U.S. customer, a significant provider of drug metabolism genotyping services to the worldwide pharmaceutical industry,” said Greg Hines, President and CEO of Tm Bioscience.

“Over the course of 2003 we expect to be able to sign additional customers for our P450-2D6 product, along with other genetic tests in our product portfolio.” The Tm Bioscience Tag-It™ Mutation Detection Kit for P450-2D6 will test for the 12 most important variants in the P450-2D6 gene. In addition to point mutations, the Kit will identify patients lacking one or both copies of the P450-2D6 gene (deletion patients) and those with multiple (greater than 2 copies) copies of the gene. More than 10% of Caucasians have mutations or a total absence of the P450-2D6 gene, resulting in significantly decreased drug metabolism, which can result in adverse drug reactions. Duplication of the gene is known to cause “ultra rapid metabolism” rendering some drugs ineffective at commonly used dosages. Hospitalization for adverse drug reactions is the third leading cause of emergency room admissions in the United States.

About Tm Bioscience – Putting the Human Genome to Work™
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 .

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