Bilateral truncal vagotomy performed in 13 rats reduced weight gain by 26% compared to controls, but also produced gastric distension. Addition of pyloroplasty was found to facilitate gastric drainage in vagotomized rats, and both procedures were then performed in 57 rats of both sexes and varying initial weights. When fed ad libitum, vagotomized animals maintained a weight 14-30% less than controls over periods of 30-300 days. When pair fed, normal rats and rats with vagotomy and pyloroplasty weighed the same. Various partial vagotomies had no effect on weight gain. It was concluded that vagotomy reduces weight gain in rats, that the reduction is the result of decreased food intake, and that the effect of vagotomy is probably not due to gastric distension.