When injected intravenously, 20 i.u. ovine prolactin significantly enhanced the output of fluid from the minimally stimulated nasal salt-gland of ducks within 5 min. This effect persisted for a further 5 min. In ducks which were still producing nasal fluid 25 min. after prolactin administration, a second enhancement of secretion was observed which could be related to an indirect effect induced by a rise in the blood glucose concentration. The initial, rapid enhancement of secretion could not be attributed to changes in blood composition and it seems possible that prolactin may have a direct effect on the avian salt-gland.