Proteins are biotechnology's raw crude. For much of its 30-year history, the industry has struggled to come up with a steady source of supply, squeezing the maximum out of these large-molecule commodities from cell lines isolated from hamster ovaries and the like. In the late 1990s--with the advent of a new class of protein-based drugs, monoclonal antibodies--demand sometimes outstripped supply. For decades, the scientists who created recombinant erythropoietin to rejuvenate red blood cells and monoclonal antibodies to combat cancer have sought out alternative forms of manufacture.

A new bioreactor--an animal genetically engineered to produce a therapeutic protein in its milk--may finally be ready to fulfill its long-awaited promise. The European Medicines Evaluation Agency (EMEA) may decide early next year on approval of an anticoagulant protein, human antithrombin, that is produced in goat's milk to treat a hereditary disorder. If the drug, ATryn, finally gets a nod from regulators, its approval will mark the culmination of a meandering 15-year journey for GTC Bio-ther-apeutics, a Framingham, Mass., spin-off of the biotech giant Genzyme.

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