Intestinal regeneration in patched intestinal defects is enhanced by both intestinal resection and urogastrone. Our aim was to determine if these two stimuli have synergistic effects. Ileal defects were patched with colon serosa in 45 rabbits. Group 1 (n = 11) were control subjects; group 2 (n = 12) underwent 50% intestinal resection; group 3 (n = 11) received urogastrone (1.5 micrograms/kg per hour subcutaneously); and group 4 (n = 11) underwent intestinal resection and received urogastrone. Animals were killed at 7 and 14 days. Intestinal resection had the greater effect on epithelialization. Urogastrone inhibited contraction and intestinal resection did not. Both intestinal resection and urogastrone increased proliferative activity. Combining intestinal resection and urogastrone did not have a synergistic effect on epithelialization and diminished the effect of urogastrone on proliferation and contraction. These findings suggest that intestinal resection and urogastrone stimulate epithelialization via similar mechanisms and that urogastrone would not enhance regeneration during intestinal adaptation.