Cardiolipin antibodies (CAb) were measured in 14 patients with primary pulmonary hypertension (PPH). These included 9 females and 5 males (mean age 36.8 +/- 9.6 years) with duration of PPH 4.9 +/- 4.1 years. No rise in CAb IgG was noted, whereas CAb IgM arose to 13.0-42.5 MPI in 3 patients. 2 lethal outcomes were registered in the group of patients with normal CAb levels and 2 in the group with elevated CAb (20% against 66.7%, respectively). The deaths were caused by progressive circulatory failure and venous occlusion, pulmonary artery embolism, respectively. It is suggested that IgM CAb increase may indicate involvement of immune disorders in PPH onset and the same nature of the mechanisms underlying some PPH subtypes and autoimmune rheumatic affections.