1. The objective of this study was to see whether another proliferative stimulus could modify the marked proliferative effect of human epidermal growth factor (urogastrone-epidermal growth factor, URO-EGF) on the gastrointestinal epithelium. 2. The response of the gastrointestinal tract to URO-EGF was investigated in rats maintained on total parenteral nutrition (TPN) with or without 75% small bowel resection. 3. Continuous infusion of 60 micrograms of recombinant beta-urogastrone/day per rat increased proliferation in the stomach by over four times (P less than 0.01), doubled proliferation in the small intestine (P less than 0.001) and increased it by four and a half times in the colon (P less than 0.001) in the control group. No significant effect of urogastrone was observed in the stomach of the resected groups, but proliferation was also increased in the small intestine by one and a half times (P less than 0.001) and by nearly four times in the colon (P less than 0.001). 4. Two-way analysis of variance showed that resection had a significant effect (P less than 0.01) on proliferation below the anastomosis and in the ileum. However, the response of the ileum was only half that observed in orally fed rats, which confirms the importance of 'luminal nutrition' in the response to resection. 5. Intestinal resection in the TPN rat was associated with a small rise in plasma enteroglucagon levels, suggesting that this hormone may be implicated in the adaptive response of the small intestine to resection.(ABSTRACT TRUNCATED AT 250 WORDS)