Patients with thromboembolism of small branches of the pulmonary artery (TESPA) were examined by rheopulmonography (RPG) for the pulmonary blood flow over the zones of thromboembolism and uninvolved parts of the lungs. The study was performed at the initial disease stage, on days 3-7 of the disease and before the patient's discharge from hospital. It was shown that pulmonary circulation undergoes some successive changes. During the first phase, the total vascular hypertension and arterial hypertension of the pulmonary circulation together with occlusion are noted. During the second phase, dilatation of the arterial bed in the healthy zones and normalization of arterial hypertension together with the reduced blood flow in the area of thromboembolism are observed. The convalescence phase is characterized by the recovery of the blood flow in the area of thromboembolism and return of the arterial tone in the pulmonary circulation to normal. RPG permits one to have an objective evaluation of the clinical picture of TESPA and therapy received by the patients.