OBJECTIVE--To determine how many lives would be saved if patients were routinely treated with ACE inhibitors after myocardial infarction according to the criteria of four recent major clinical trials, and to estimate the costs and benefits of these approaches. DESIGN--Retrospective survey. SETTING--The Nottingham Health District. PATIENTS--Data from 7855 patients admitted between 1989 and 1990 were combined and the selection criteria of four major clinical trials (AIRE, SAVE, GISSI-3, and ISIS-4) were applied. RESULTS--Of the patients admitted in Nottingham with confirmed myocardial infarcts 39% were eligible for AIRE and 8% for SAVE. In patients with suspected myocardial infarction as defined by the major trials, 60% would have been eligible for GISSI-3 and 63% for ISIS-4. Treating appropriate patients in accordance with these trials would have saved 20 (AIRE), 3 (SAVE), 4 (GISSI-3) and 5 (ISIS-4) lives each year in Nottingham at a drug cost of 5400 pounds, 33 pounds 791, 2730 pounds, and 4116 pounds per life per year saved respectively. CONCLUSIONS--Short-term treatment with ACE inhibition appears to be cheaper but such an approach would save fewer lives. The AIRE study is the most applicable to current clinical practice but ACE inhibitors should be offered routinely to patients satisfying the criteria of any of the four major clinical trials.