The aim of the following study was to gain some insight into the functional characteristics of different portions of the small intestine after either partial resection or syngeneic and allogeneic transplantation 3 months postoperatively. Nutritional parameters (serum albumin levels, serum triglyceride levels, maltose absorption, excretion of fecal fat) and fat-stimulated neurotensin release were determined in Lewis rats that underwent small-bowel resection (n = 21), syngeneic (Lewis-->Lewis, n = 21), or allogeneic transplantation (Brown Norway-->Lewis, n = 24). The length of the remnant, isograft, or allograft was 27 cm (i.e., one-third of the rat small intestine) and consisted of the proximal (n = 7), middle (n = 7), or distal (n = 7) portion. Three postoperative deaths were due to ileus or pneumonia. After allotransplantation cyclosporine (15 mg/kg body wt. s.c.) was administered for graft acceptance. The control group was not operated upon, but was composed of weight- and age-matched Lewis rats (n = 7). We found that resection of two-thirds of the small intestine led to significantly lower levels of albumin and triglycerides in all three portions investigated (P < 0.01), but did not affect maltose absorption. Excretion of fecal fat was elevated significantly only after distal resection (P < 0.05). When compared to resected animals, syngeneic transplantation did not affect the nutritional parameters, but caused a significantly higher hormone release (P < 0.05) in all three different intestinal grafts. Allogeneic transplantation was successful when the middle or distal portion was grafted. All recipients of proximal allografts showed a severe loss of body weight and died between day 8 and 10 after transplantation.(ABSTRACT TRUNCATED AT 250 WORDS)