It has been reported that: 1) ovine growth hormone stimulates intestinal water, sodium, and chloride absorption and 2) specific growth hormone receptors are present in the rat intestine. Aims of this work were to investigate the effects of acute administration of hGH on water and ion transport in the rat ileum in vivo and in vitro. In vivo, the absorption rates of water, sodium, chloride, and potassium were determined in the rat perfused ileum, during a basal period and after i.v. administration of 6 micrograms/kg recombinant DNA-derived hGH. In vitro, electrical parameters were measured before and after the hormone addition to the mucosal or the serosal side of rat ileal mucosa mounted in Ussing chambers. In vivo, growth hormone induced a rapid increase in the absorption rates of water, sodium, chloride, and potassium. In vitro, the serosal, but not the mucosal, addition of growth hormone induced a rapid decrease of transepithelial potential difference and of short-circuit current. The effect was time- and dose-dependent, saturable, but not reversible in the short time. The electrical effect was abolished in the absence of chloride, indicating that it was related, at least in part, to inhibition of basal active chloride secretion. Growth hormone also reduced the short-circuit current increase induced by the secretagogues Escherichia coli heat-stable enterotoxin, theophylline, and calcium ionophore A23187. These results indicate that hGH has a rapid absorptive effect that is related, at least in part, to a direct intestinal antisecretory mechanism. It also reduces active intestinal secretion induced by various secretagogues.