Background/Aims: Cholecystokinin (CCK) inhibits gastric emptying and may exert satiety effects in several species, including humans. Because the effects of physiological doses of CCK on satiety in humans is unclear, the satiety effects of CCK-33 in physiological levels in lean and obese subjects were studied. Methods: CCK-33 was infused intravenously to 32 healthy men or women (14 obese, all women; 18 lean, 4 men and 14 women) in doses that elicited plasma CCK concentrations in the physiological range. The effects of these infusions on feelings of hunger, wish to eat, fullness, and prospective feeding intentions were measured on visual analogue scales and compared with saline during a 1-hour infusion period. Results: The CCK infusions induced significant decreases in hunger feelings, wish to eat, and prospective feeding intentions (P < 0.05), whereas fullness tended to be increased (P = 0.054). No clear differences between lean and obese subjects were observed apart from a more marked decrease in fullness and increase in prospective feeding intentions during the 1-hour saline infusion in the lean group (P < 0.05). Conclusions: CCK infusion leading to physiological plasma levels significantly increases satiety in humans.