Stress (heat shock) proteins are ubiquitous intracellular proteins that can be induced in vitro by physiological stress events that occur during inflammation. We have used an indirect immunoperoxidase method to locate 60-kDa stress proteins in biopsies taken from normal and inflamed colorectal mucosa. An anti-60-kDa monoclonal antibody (ML30) produced specific staining of surface epithelial cells localized to the site of the Golgi apparatus. In ulcerative colitis, there was an increased concentration of this stress protein compared with controls (P < or = 0.002) and also with a small group of active Crohn's colitis (P < or = 0.01), but no relationship between its concentration and disease activity. All biopsies also showed staining of goblet cells by ML30, suggesting a possible cross-reaction with mucin; electroblotting of crude but not purified mucin showed a faint 60-kDa band with ML30. We conclude that the 60-kDa stress protein is present in normal colorectal epithelial cells and is markedly induced in vivo in ulcerative colitis. Further, we suggest that since the 60-kDa protein functions as a molecular chaperone, it may associate with colonic mucin aiding in its synthesis and/or secretion.