Luminal nutrition is known to have a trophic effect on small bowel mucosa after intestinal resection. Humoral agents, however, may also contribute to this process. Two of the proposed humoral agents, enteroglucagon and gastrin, were therefore investigated after intestinal resection and transection in the rat, and changes in their concentration in the plasma were related to cellular proliferation. Forty-eight male Wistar rats had either 75 per cent proximal small bowel resection or jejunal transection. The animals were further divided into three groups, each with a different nutritional intake. The first group were allowed food ad libitum. The second group were kept under hypothermic conditions which resulted in hyperphagia, while the last group were nourished intravenously. A further 8 animals had a laparotomy only (sham operation). All animals were killed 12 days after operation, plasma enteroglucagon and gastrin were measured, while determination of the crypt cell production rate (CCPR) was used to denote cellular proliferation. In each group resected rats had significantly higher crypt cell production rates and greater enteroglucagon levels compared with transected animals. However, only in the normally fed group was plasma gastrin increased in resected animals, there being no significant difference in the plasma concentration of this peptide in transected compared with resected rats, in both the intravenously fed and hyperphagic groups. In the models studied enteroglucagon appears to be a more likely candidate for a humoral trophic agent than gastrin in intestinal adaptation.