The hypothesis that glucagon 1-21 (G1-21) is trophic to the gastrointestinal tract was investigated in the hypoplastic intestine of intravenously maintained rats. Three groups of eight rats were fed parenterally for three days and then were infused with either 0, 20 or 80 micrograms rat-1 day-1 of G1-21 for 3 days. No significant effect on the weight of the stomach, caecum or colon was observed, but both the weight and crypt cell production rate of the small intestine were significantly decreased by G1-21. Plasma enteroglucagon was also decreased by G1-21 treatment. It is concluded that G1-21 does not have a trophic effect on the gastrointestinal tract, and, in fact, has an antiproliferative effect on the small intestine, which could in turn be modulated by decreased levels of endogenous enteroglucagon.