This study was conducted to determine if lower dose heparin (LD Heparin) combined with aspirin is as efficacious as higher dose heparin (HD Heparin) for the treatment of the antiphospholipid antibody syndrome in women seeking pregnancy. The method of the study was a prospective, single center trial including 50 patients who were consecutively assigned to treatment. Each patient had at least three consecutive, spontaneous pregnancy losses, positive antiphospholipid antibodies on two occasions, and a complete evaluation. Data were compared using Fisher's exact test. Viable infants were delivered from 20/25 (80%) women treated with higher dose heparin vs. 19/25 (76%) of women treated with lower dose heparin. There were no significant differences between groups with respect to gestational age at the time of delivery (37.2 +/- 3.4 versus 37.7 +/- 1.6 weeks), maternal complications, or fetal complications. A lower dose of heparin plus aspirin was as effective as higher dose heparin for the treatment of antiphospholipid antibody-associated recurrent pregnancy loss.