102 patients at high risk of pre-eclampsia and/or fetal growth retardation were randomly allocated to treatment with 300 mg dipyridamole and 150 mg aspirin daily from 3 months' gestation onwards (group A) or to the control group (group B, no treatment). Group A was twice as likely as group B to have a normal pregnancy. Pre-eclampsia occurred in 6 patients in group B and none in group A. Major complications (fetal death or severe growth retardation) occurred in 9 patients in group B and none in group A. Platelet count and plasma volume were significantly higher in group A than in group B throughout pregnancy. The treatment did not produce serious adverse effects. Antiplatelet therapy given early in pregnancy to high-risk patients may thus protect against pre-eclampsia and fetal growth retardation.