Forty rats were used to examine the effect of plane of nutrition on the growth response of rate to castration. Rats were offered 8, 12, 16 or 20 g/rat/day of a commercial small animal feed. Castration depressed feed consumption, growth rate, efficiency of feed utilization and carcass mass and protein content. The influence of castration increased as plane of nutrition improved. The results indicated that the effect of castration on growth of rats may be attributable almost entirely to an effect on appetite.