Maternal lupus anticoagulants and anticardiolipin antibodies are associated with a syndrome of recurrent pregnancy loss or preterm birth in live-borns, fetal growth retardation, and placental infarction. Fourteen women with one or more abnormal pregnancy outcomes (total 28 losses, one severely growth-retarded premature live-born) and no normal outcomes were treated with full-dose, subcutaneous, twice-daily heparin therapy in subsequent pregnancies. Treatment was started at an estimated gestational age of 10.3 +/- 4.0 (mean +/- SD) weeks (range 6-18), in a mean total daily dosage of 24,700 +/- 7400 units (range 10,000-36,000). Fourteen of 15 pregnancies resulted in live births at 36.1 +/- 1.7 weeks (range 33-39). The mean birth weight percentile was 57 +/- 21 (range 10-90), and Apgar scores were good to excellent. The number of placental infarcts was fewer in treated cases than in previous deliveries. Five fetuses had third-trimester or perinatal problems with no sequelae, four discovered by close maternal-fetal monitoring. There was an increased rate of preterm and cesarean deliveries. Maternal complications of treatment were few and minor, with no hypertension, preeclampsia, or serious drug-related complications. Heparin appears suitable for further investigation in the treatment of this obstetric syndrome.