Low-dose aspirin does not influence the clinical course of women with mild pregnancy-induced hypertension. The effect of low doses of aspirin on women with mild pregnancy-induced hypertension was investigated by means of a prospective, randomized, double-blind trial. Forty-seven women hospitalized at 30-36 weeks' gestation because of mild pregnancy-induced hypertension were treated by a daily dose of either 100 mg aspirin or placebo. The mean blood pressure values, rates of development of severe preeclampsia, gestational ages at delivery, newborn weights, and 5-minute Apgar scores were similar in the aspirin-treated and the placebo-treated groups. We conclude that low-dose aspirin is not curative but is essentially a preventive treatment which, in order to be effective, should be started weeks before clinical signs of preeclampsia are present. 