The relationship between operative procedures and the incidence of remnant stomach carcinoma was investigated in male Wistar rats orally treated with N-methyl-N'-nitro-N-nitrosoguanidine [(MNNG) CAS: 70-25-7; 1-methyl-3-nitro-1-nitrosoguanidine]. A total of 178 rats was divided into 5 groups: After gastrectomy in which half of the glandular stomach was removed, group 1 received Billroth II reconstruction; group 2 was given short Roux-en-Y reconstruction; group 3 had long Roux-en-Y reconstruction; group 4 received gastrotomy alone; and group 5 consisted of nonoperated control rats. The incidence of gastric adenocarcinoma in MNNG-treated rats was significantly higher in group 1 (38.9%) as compared with that in group 3 (7.1%) and that in group 5 (9.5%). All tumors developed in the gastroenteric anastomotic area. Histologic examination of the gastric mucosa revealed atrophic gastritis and erosion in the gastroenteric anastomotic area, especially in rats with carcinoma. These findings seem to implicate the duodenogastric reflux, especially the reflux of bile acids, in the development of remnant stomach carcinoma in rats.