Numbers of intestinal goblet cells containing specific acid mucins were determined in male Sprague-Dawley rats receiving azoxymethane (total dose 90 mg kg-1) with or without jejunoileal bypass (JIB). Controls had injections of vehicle and sham bypass. Thirty weeks postoperatively colorectal length and crypt depth were increased by azoxymethane and further increased by JIB. JIB doubled the yield of intestinal tumours (P less than 0.01). Goblet cells containing sulphomucins normally predominated throughout the intestinal tract. Contents of sulphomucins and especially sialomucins were consistently higher in the small bowel and colon of rats receiving azoxymethane alone, but again the highest values were observed in animals with azoxymethane plus JIB. Both small-bowel bypass and azoxymethane stimulate adaptive growth of the colon and small bowel remaining in circuit. Goblet-cell hyperplasia is a feature of this response, and sialomucins are preferentially secreted by the adapting epithelium.