Undifferentiated connective tissue disease with secondary antiphospholipid syndrome was diagnosed in a 33 year old woman after recurrent arterial thromboses, two miscarriages and myocarditis. Despite effective immunosuppression and anticoagulation her initially mild precapillary pulmonary hypertension progressed in the absence of thromboembolic events, cardiopulmonary disease or other systemic disorders. With continuous i.v. iloprost in a dosage of up to 4.5 ng/kg/min for a total of 15 months, her 6 min walking-distance improved from 210 to 315 m, the pulmonary vascular resistance decreased from 1710 to 1111 dyn x s x cm-5 and the mean pulmonary arterial pressure decreased from 64 to 54 mmHg. This partial success of conservative treatment enabled a reassessment of the necessity for heart and lung transplantation.