From studies in animals and humans it is known that individual satiety signals can interact: contributions of glucagon and CCK produced functionally synergistic inhibitions of feeding in rats, that is, simultaneous injection of the two peptides inhibited feeding significantly more than the sum of their individual effects. In contrast, we have been unable to show in healthy volunteers any interaction between GLP-1 and CCK33; the simultaneous infusion of CCK33 and GLP-1 resulted in an infra-additive reduction in meal size, which led us to suggest that the two peptides could even interact antagonistically.