13,634 patients entering 650 Chinese hospitals up to 36 h after the onset of suspected acute myocardial infarction (MI) were randomised between one month of oral captopril (6.25 mg initial dose, 12.5 mg 2 h later, and then 12.5 mg three times daily) or matching placebo. Captopril was associated with a non-significant reduction in 4-week mortality (617 [9.05%] captopril-allocated vs 654 [9.59%] placebo-allocated deaths; 2p = 0.3). There was a significant excess of hypotension, mostly early after the start of treatment, but no evidence of any adverse effect on early mortality (even among patients who were hypotensive at entry). Taken together with the other trials of converting enzyme inhibitors started early in acute MI, these results indicate that such therapy is generally safe and typically prevents about 5 deaths per 1000 patients treated for the first month.