W e examined the effect of intravenously infused glucagon-like peptide 1 (GLP-1) on subjective appetite sensations after an energy-fixed breakfast, and on spontaneous energy intake at an ad libitum lunch. 20 young, healthy, normal-weight men participated in a placebo-controlled, randomized, blinded, crossover study. Infusion (GLP-1, 50 pmol/ kg.h or saline) was started simultaneously with initiation of the test meals. Visual analogue scales were used to assess appetite sensations throughout the experiment and the palatability of the test meals. Blood was sampled throughout the day for analysis of plasma hormone and substrate levels. After the energy-fixed breakfast, GLP-1 infusion enhanced satiety and fullness compared with placebo (treatment effect: P < 0.03). Furthermore, spontaneous energy intake at the ad libitum lunch was reduced by 12% by GLP-1 infusion compared with saline (P = 0.002). Plasma GLP-1, insulin, glucagon, and blood glucose profiles were affected significantly by the treatment (P < 0.002). In conclusion, the results show that GLP-1 enhanced satiety and reduced energy intake and thus may play a physiological regulatory role in controlling appetite and energy intake in humans.