This study examined the effect of chronic infusions of insulin in one of three doses (5, 7.5 or 10 mU/day) into the third ventricle, on food and water intake and body weight in the rat. Solutions were infused via osmotic minipumps at a rate of 1 microliter/hour for seven days. The two highest doses of insulin produced a dose-related suppression of food intake and weight loss, which was greater than the effect produced by 5 mU/day or a control infusion of Ringers solution. The effect of 5 mU/day on food and water intake and body weight was similar to the effect of the control infusion. All groups treated with insulin decreased food intake during the day and night, although only differences in nighttime food intake were statistically significant. Ten mU/day also produced a significantly greater reduction in water intake than each of the other solutions. Weight loss in the animals infused with insulin could not be explained by a decrease in caloric intake alone. Food intake returned to normal in all groups by the end of a seven day post-infusion period, with recovery being slowest among the animals receiving the highest doses of insulin. All animals recovered body weight at approximately the same rate. These results provide further evidence for the view that brain insulin plays a role in the regulation of food intake and body weight.