This study was carried out to investigate the effects of human neuropeptide Y (NPY), administered intraperitoneally (i.p.) or orally on food intake and growth of tilapia Oreochromis niloticus (11. 19 g) in two separate experiments. In the first experiment, which lasted for 24 It, NPY was injected intraperitoneally (i.p.) at 0, 0.1, 0.3, 0.6 mu g g(-1) body weight (bw). In the second experiment, NPY was given orally at 0, 0.125 and 0.25 pg g(-1) feed for 50 days.