We have reported that intravenous bombesin decreases single meal size in a dose-dependent manner. The present study tests whether intraventricular bombesin is also effective in decreasing single meal size. Doses of bombesin (0.1-4 micrograms/kg) were administered both intravenously and intraventricularly. A median dose of 1 microgram/kg bombesin decreased 30 min meal size about 50%, whereas a median dose of 1 microgram/kg given intravenously only decreased meal size 25%. We conclude that bombesin given centrally in the baboon can decrease meal size and that this effect does not appear to be due to leakage into the periphery.