All 98 cases of sulfonylurea-induced hypoglycemia reported by the 30 regional drug-monitoring centers between 1985 and 1990 were analyzed: 46 with gliclazide, 40 with glibenclamide, 5 with glipizide, 1 with glibornuride and 6 with first-generation sulfonylureas. These cases of hypoglycemia were often serious. The patients were 61% female and their mean age was 78.9 years. The average number of medications being taken was 3.4, but ranged up to 14. The risk factors were: reduced food intake (4.2%), renal failure (4.2%), prescription error (3.2%), voluntary or accidental overdose (5.2%), alcohol (1.1%), suspected drug interactions (50%), unknown (32.6%). The most frequent drug interactions involved miconazole (8 cases), angiotensin-converting enzyme inhibitors (9 cases), lipid-regulating agents (fibrates) (7 cases), co-trimoxazole (trimethoprim-sulfamethoxazole; 5 cases), metformin (4 cases), histamine H2-receptor antagonists (4 cases). The mechanisms of these interactions are discussed.