Cannulas aimed at the lateral cerebral ventricles were surgically implanted in baboons. A-II [angiotensin II] (5 .mu.g/animal) or control injections were made on subsequent days and water intake recorded to determine the patency of the cannulas. Baboons drink considerable water after intraventricular administration of A-II. The response diminishes but still persists with repeated A-II tests spread over a several-month interval. Elevated drinking in response to the administration of A-II is a practical way to confirm the success of ventricular cannulation.