The subject invention provides novel peptides for use in treating mammals to control appetite and obesity. Disclosed is a peptide derivative having the formula: X.sup.1-Z-Q-arg-trp-NH.sub.2 wherein: X.sup.1 is an acyl group, Z is amino-2-naphthyl-carboxylic acid or histidine, Q is (D)phenylalanine or p-iodo-(D)phenylalanine, or a pharmacologically acceptable salt, complex or derivative thereof, the peptide derivative having melanocortin-4 receptor agonist activity.