After two daily ovine prolactin injections in rats, significant increases in jejunal absorption of glucose, glycine and proline, as well as of fluid and NaCl, occurred. Although ouabain caused dramatic reductions in fluid, sodium, chloride and glucose transport, prolactin had an effect even in the presence of ouabain. Mucosal hypersomolaity significantly decreased fluid, sodium and chloride absorption but had no significant effect on glucose transport. Addition of prolactin in vitro had no effect on intestinal absorption. Prolactin-induced increases in transport of fluid, NaCl and organic nutrients by the mammalian jejunum may play an important role in nutritional and osmoregulatory adaptations.