Primary sclerosing cholangitis (PSC) is an uncommon, chronic disorder characterized by inflammatory fibrosis usually involving the entire biliary tree. The etiology has been unknown, but PSC is closely associated with ulcerative colitis, which coexists in more than two thirds of patients with PSC. In recent studies 3% to 5% of all patients with ulcerative colitis had PSC. We propose that PSC is, at least in part, an immunologically mediated disease; it is closely associated with human leckocy...