The effect of postoperative parenteral nutrition on the healing of abdominal wall wounds and colonic anastomoses in protein-malnourished rats was studied. The healing of laparotomy wounds and colonic anastomoses was assessed by bursting pressure measurement on the fifth postoperative day. Compared with control animals on a normal diet (group A), rats on a low-protein diet given postoperative dextrose-saline solution (group B) had significantly lower abdominal wall and colonic anastomotic bursting strengths. The detrimental effects of protein malnutrition could be completely reversed for abdominal wall wounds and partially reversed for colonic anastomoses in rats on a low-protein diet given postoperative parenteral nutrition (group C). Autoradiographic studies showed a marked decrease in the activity of wound fibroblasts that was restored by the administration of postoperative parenteral nutrition. Serum protein measurements showed a closer correlation of colonic anastomotic healing to serum albumin than to serum transferrin values but showed no correlation with abdominal wall wound healing.