This review summarizes the evidence from five of the larger randomized controlled trials evaluating the effects of angiotensin converting enzyme inhibitors started in the early phase of myocardial infarction on subsequent mortality and major morbidity. Altogether, information on about 98,000 patients is available from these trials. In four studies, trial treatment was started within 24 h, and in one study within 36 h, of the onset of symptoms of acute myocardial infarction, and mortality was assessed after a few weeks or months of treatment. When taken together, these trials show that angiotensin converting enzyme inhibitors produce a significant 7% relative risk reduction in mortality (P < 0.006), which corresponds to an absolute difference of about five fewer deaths per 1,000 patients treated. The benefits may be greater in higher-risk patients (e.g. those with previous myocardial infarction, heart failure or large infarcts). These results demonstrate that for a wide range of patients without clear contraindications, angiotensin converting enzyme inhibitors started early in acute myocardial infarction prevent further deaths in the first few weeks when added to standard therapy (aspirin, thrombolytic therapy and beta-blockers). The early benefits seen with ACE inhibitors seems to persist for at least the first year. The clinical implications of these results are discussed.