In a group of 10 women with circulating lupus anticoagulant 25 intrauterine deaths were previously documented in the nine multigravidae. The presence of lupus anticoagulant activity was confirmed by showing prolongation of the activated partial thromboplastin time and kaolin clotting time with failure of correction of the prolongation on incubation with normal plasma. A clinical diagnosis of systemic lupus erythematosus (SLE) was made in four women. Three had deep vein thrombosis in pregnancy, one chorea gravidarum while two had only recurrent fetal losses. All the women had positive antinuclear antibody tests and blood platelet counts less than 175 X 10(9)/l. Anti-smooth muscle antibody and VDRL tests were each positive in half the patients; anti-DNA antibody was present in two patients with clinically active SLE. In six pregnancies correction of the activated partial thromboplastin and kaolin clotting time was attempted using prednisone (40-60 mg/day); aspirin, 75 mg/day, was added. Five live infants were obtained, four by spontaneous delivery, when the restoration of the clotting abnormalities to normal was achieved. In one woman presenting with extensive deep vein thrombosis a live infant was delivered following therapeutic doses of heparin and low dose aspirin. Maternal lupus anticoagulant activity has major implications for pregnancy and should be excluded in women with a clinical suspicion of SLE, a positive antinuclear antibody test, thrombotic episodes, biologically false-positive VDRL and unexplained late or repetitive early fetal losses.