This study, conducted in Auckland, New Zealand, over 2 years from March 1986, used a case-control design to investigate the hypothesis that alcohol acutely increases the risk of both nonfatal myocardial infarction and coronary death in the 24 hours after drinking, among regular drinkers. The nonfatal myocardial infarction analyses included 278 male and 60 female cases identified from a population-based coronary heart disease surveillance program and 458 male and 266 female controls randomly selected from the same population matched by age and sex. In the coronary death analyses, 172 male and 16 female coronary death cases from the same surveillance program and a population-based sample of 294 males and 165 females who were age and sex matched were examined. Information on alcohol consumption in the 24 hours before the coronary event in cases and a comparable 24-hour period in controls was collected. Study subjects all drank alcohol regularly at least once per month and were aged 25-64 years. Controls were more likely than cases to report a drinking episode in the 24-hour period examined in both sexes and for fatal and nonfatal disease. After controlling for possible confounding, the authors found that drinkers had a consistently lower estimated risk of both fatal and nonfatal coronary heart disease than participants reporting no alcohol in the previous 24 hours. The odds ratios ranged from 0.75 (95% confidence interval 0.62-0.90) for nonfatal myocardial infarction in men to 0.46 (95% confidence interval 0.19-1.10) for coronary death in women. There were no clear differences in estimated acute risk among those who drank one or two drinks, three or four drinks, or more than four drinks in the 24-hour period. These findings suggest that, contrary to previous speculation, alcohol consumption may acutely reduce coronary heart disease risk.