The effects of neuropeptide Y (NPY) on release of growth hormone (GH) and gonadotropin (GTH) from the goldfish pituitary in vitro were investigated. Exposure of perifused pituitary fragments, taken from female goldfish at late stages of gonadal recrudescence, to 5-min pulses of human NPY resulted in a rapid dose-dependent stimulation of GH and GTH release, with half-maximal effective dosages of 0.51 ± 0.24 and 2.37 ± 1.05 n M for GH and GTH, respectively. Repeated treatments with pulses of NPY (10 n M for GH, 5 n M for GTH) at 55-min intervals did not significantly alter the responsiveness of pituitary fragments to NPY; however, prior exposure of pituitary fragments to pulses of higher doses of NPY (50 n M GH, 10 n M for GTH) significantly reduced the subsequent hormone responses. When given at 85-min intervals repeated treatment with NPY did not blunt hormone responses to the second and third stimulations at these higher dosages. These results indicate that NPY acts at the pituitary level to stimulate GH and GTH secretion in female goldfish. The GTH response and, to a lesser extent, the GH response become desensitized to further stimulation by NPY in dose- and time-dependent manners. NPY should be considered as one element in the multifactorial systems regulating the GH and GTH secretion in goldfish.