Objective: To investigate the hemodynamic state in the ovarian hyperstimulation syndrome (OHSS) in the rabbit model and to determine the role of angiotensin II in the pathophysiology of this syndrome. Design: Experimental study. Setting: Physiology laboratory. Animal(s): Female New Zealand rabbits were studied; 16 rabbits were stimulated with gonadotropins, and 6 were controls. Six of the stimulated rabbits received additional treatment with captopril. Main Outcome Measure(s): Cardiac index, blood pressure, and heart rate were recorded. Result(s): Gonadotropin-stimulated rabbits had significant enlargement of ovaries that was not modified by captopril. Ascites was present in 80% of animals in the OHSS group; captopril significantly decreased the incidence and volume of ascites. The three groups did not differ in blood pressure, heart rate, cardiac index, and total peripheral resistance. Conclusion(s): In rabbits with OHSS, ascites are a primary event. Such animals are normotensive and have normal vascular resistance and cardiac index. Angiotensin-converting enzyme inhibition decreases the incidence of OHSS in the rabbit model by 30%, suggesting that angiotensin II may play a role in the formation of ascites.