In rats, modafinil, an alpha1 adrenergic receptor dependent, that has been shown to increase wakefulness without subsequent rebound effect, decreases feeding and reduces body weight. However, modafinil does not show a monotonic dose-related decrease in food intake. The dose-response curve for modafinil is U-shaped; feeding decreases after doses of 20 and 40 mg/kg, but no effects were seen after doses of 10 and 80 mg/kg. When feeding is resumed, no compensatory effect is seen, and body weight remains lower during the 24-h session. The drinking-to-feeding ratio remains unchanged, showing that modafinil has no effect on water intake. These results are discussed with reference to the possible mechanisms underlying the relation between sleep, feeding, and metabolism.