The involvement of endogenous opioids in control of human food intake and appetite was investigated in a double-blind placebo-controlled study using a single, 2.5 mg oral dose of the opioid receptor antagonist, nalmefene. Ratings of the pleasantness of the smell and the taste, but not the appearance, of a number of foods was significantly lower in nalmefene-treated subjects. The magnitude of this effect was greater in food items independently rated as highly palatable. Caloric intake of a buffet-style meal was 20% lower in nalmefene-treated subjects, with the proportional reduction in intake of individual food items also depending on their palatability. These results lend further support to recent suggestions that opioids are involved in reward-related aspects of ingestion.