This study was undertaken to find a relationship between cardiac function indices and endocrine functions during prostaglandin E1 induced hypotension in surgical patients. Thirteen patients who underwent either orthopedic or gynecologic surgery were the subjects of the study. Systolic blood pressure decreased to 80 torr with prostaglandin E1 infusion (0.5-2 micrograms.kg-1 x min-1) under enflurane-N2O anesthesia. The cardiac function were judged by transesophageal echo-cardiography. Plasma ANP and ADH levels were measured by radioimmunoassay. Significant reductions in the left atrial diameter and A/R and significant increases in cardiac output were observed, but there were no significant changes in fractional shortening and pulmonary vein flow. Plasma ANP concentrations decreased significantly from 45.3 +/- 5.1 pg.ml-1 (mean +/- SE) of pre-hypotension to 32.6 +/- 2.2 pg.ml-1 of control, but plasma ADH levels increased significantly during hypotension (P < 0.05). We could not find any significant correlation between the cardiac function indices and plasma hormone levels. Transesophageal echocardiography is an excellent monitor during induced hypotension. It is difficult to predict the ANP and ADH levels by measuring cardiac function as judged by TEE.