Specific growth hormone (GH) receptors are located along the entire rat intestine. We have recently shown that GH induces water and ion absorption in the rat ileum. This raises the possibility that GH regulates water and ion transport throughout the intestine. To test this, we have evaluated the effects of GH administration on jejunal, ileal, and colonic water and ion transport, by the in vivo rat perfused intestine, and in vitro, in corresponding segments of intestine mounted in Ussing chambers. In vivo, GH increased water absorption by 250%, 180%, and 80% over baseline in the jejunum, ileum, and colon, respectively. The effect had similar kinetics in the three intestinal regions. In vitro, serosal GH administration induced a decrease in short-circuit current, consistent with an absorptive effect. The effect showed a proximal to distal decreasing pattern. These findings suggest that GH plays a role in the body fluid homeostatic control, promoting water and ion absorption.