Plasma renin activity (PRA), angiotensin II (ATII), aldosterone (ALD) and atrial natriuretic factor (ANF) were determined in 30 patients with high altitude myocardial hypoxidosis (HAMH) with radioimmunoassay and the data were compared with those of 40 healthy subjects and 26 patients with high altitude chronic cardiopathy (HACC). All of them have been in Lasa, a place with an altitude of 3,658 meter, for a long time. The results showed that PRA and plasma ATII increased significantly (P < 0.05-0.01) and plasma ANF decreased significantly (P < 0.01) in patients with HACC and were higher than those in the control. It is suggested that disturbance of these biologically active substances might play a role in the development of HAMH.