We evaluated the effects of systemic delivery of amphibian bombesin and its mammalian homologues on the length of the postprandial intermeal interval. Adult male rats, feeding ad libitum, were injected intraperitoneally (i.p.) 5 min after the end of the first nocturnal meal with 0 (vehicle), 2.5, 5, or 10 nM/kg of tetradecapeptide bombesin (BN), gastrin-releasing peptide(1-27) (GRP1-27), the C-terminal decapeptide of GRP(18-27) (GRP18-27), the C-terminal decapeptide of neuromedin B (NMB23-32), or combinations of equimolar doses of GRP1-27 and NMB23-32. BN produced a potent, dose-related extension (maximum of 177%) of the first postprandial intermeal interval; GRP1-27 produced a lesser but significant prolongation (maximum of 47%); the combination of GRP1-27 and NMB23-32 produced an intermediate prolongation (maximum of 70%); GRP18-27 alone and NMB23-32 alone failed to produce any significant change. Peptide effects were limited to the first postprandial intermeal interval. The results demonstrate that systemic, postprandial injection of BN, GRP1-27, or the combination of GRP1-27 and NMB23-32 extends the duration of the postprandial intermeal interval. The results suggest that the endogenous peptides, released in the gastrointestinal tract by ingested food, have a potent satiety action, selectively lengthening the intermeal interval.