A large co-ordinated multinational clinical-trial programme in hypertension has provided comparative data on adverse events in patients on lisinopril (n=318) compared with enalapril (n=321) and in 230 patients on lisinopril versus captopril (n=235). The three groups were demographically well matched with regard to age and duration of treatment. However, in comparison with the lisinopril group, the captopril-treated group had a slightly higher proportion of males (NS). The incidence of adverse events on lisinopril was similar to that on enalapril (10.4vs.8.7%, NS)andcaptopril(11.7vs. 11.9%, NS). The incidence of withdrawals was similar on lisinopril and enalapril (1.9 vs. 1.9% NS) and captopril (4.8 vs. 3.0% NS). The most frequently reported events affected the digestive, respiratory, or nervous and psychiatric systems of the body. The pattern of events and withdrawals was similar for all three drugs. The incidence of laboratory changes for lisinopril versus enalapril and lisinopril versus captopril was similar. The safety profiles of all three drugs were comparable in young and elderly patients. First-dose hypotension was reported for 2 of 548 patients on lisinopril, and renal failure was reported for 3 of 286 patients on enalapril. Overall, the events reflected the class-specific effects previously identified for angiotensin-converting enzyme inhibitors. The data indicate that long-acting angiotensin-converting enzyme inhibitors do not impose any additional side-effect risk in hypertension.