The roughly five million Americans who suffer from heart failure, a chronic and deadly disease, could be part of a radical change in the practice of medicine later this year. Cardiologists across the country will likely begin to prescribe a new, and by most accounts highly promising, drug based on an unusual criterion: whether the patient is black or white -- or, to be more precise, whether the person identifies him- or herself as an African American.

Sometime by midyear, the U.S. Food and Drug Administration will decide whether to approve BiDil, a heart failure medicine developed by NitroMed, a small pharmaceutical company in Lexington, MA. Experts say that the drug, if approved, will be the first pharmacuetical targeted exclusively at a specific racial group. While physicians often prescribe medicines differently for white and black patients, the new pill could mark a change in how drugs are clinically tested, reviewed by the FDA, and marketed. And its arrival has set off a heated debate among physicians, geneticists, and social scientists over the biological justification for and social ramifications of so-called race-based medicines -- and over how drug developers should handle information about genetic variations in the world's different populations.