The present review summarizes the appetite suppressing effects of PYY and GLP-1 in the regulation of food intake in humans. Current evidence supports a role for gastrointestinal peptides as regulators of satiety. The regulation of satiety is, however, complex and it is not surprising that multiple control systems exist. It is interesting to note that nutrients in the small intestine such as hydrolysis products of fat stimulate the release of satiety peptides such as GLP-1 or PYY that serve as satiety signals. Both peptides, released from L-cells from the gastrointestinal tract by the local action of digested food, exert various regulatory functions: stimulation of insulin secretion and inhibition of glucagon secretion as typical actions of GLP-1, inhibition of gastric emptying, and inhibition of appetite for both GLP-1 and PYY. The review focuses on the question, whether the two peptides are true endocrine factors that act as physiologic, hormonal regulators of appetite.