The risks of agranulocytosis and aplastic anemia in relation to the use of cardiovascular drugs were estimated in a population-based case-control study conducted in Israel and Europe (total population, 23 million). Cardiovascular drug use in the week before onset of illness was compared between 270 patients hospitalized with agranulocytosis and 1870 hospitalized control subjects. Propranolol (relative risk, 2.5), dipyridamole (3.8), digoxin (2.5), and acetyldigoxin (9.9) were significantly associated with agranulocytosis. The excess risks attributable to these drugs ranged from one to three cases per 10 million persons exposed for up to 1 week. Increased risks were also observed for cinepazide (used by six cases and no control subjects), procainamide (7, 1), and aprindine (5, 1); based on crude relative risk estimates, the excess risks for the latter two drugs were approximately three per million persons exposed for up to 1 week. The use of cardiovascular drugs in a 5-month period ending 1 month before hospital admission was compared between 152 patients with aplastic anemia and 2180 control subjects. Furosemide was the only significantly associated drug (relative risk, 3.1); the excess risk attributable to any exposure in a 5-month interval was 1.7 per million.