We report here two cases of recurrent miscarriages that were successfully treated with continuous intravenous administration of low molecular weight heparin (LMWH). One patient experienced 11 spontaneous abortions, and the other eight abortions. Previous treatments including prednisone, aspirin and mononuclear-cell immunization were all unsuccessful. They were negative for anticardiolipin antibodies and lupus anticoagulant, and had no inherited thrombophilic disorder. Intravenous administration of LMWH, 4800 units of dalteparin, was started as soon as the conception was confirmed, and was continued until 34 weeks of gestation. They were delivered of live born infants.