Perinuclear antineutrophil cytoplasmic antibodies (pANCAs) have previously been demonstrated in patients with various forms of vasculitis and more recently in those with inflammatory bowel disease (IBD) by an indirect immunofluorescence technique. Sera from 194 patients were tested for pANCAs: 101 with ulcerative colitis (43 with varying grades of disease severity, 19 after subtotal colectomy, 39 following restorative proctocolectomy), 40 with Crohn's disease, five with indeterminate colitis, 24 patients without IBD and 24 healthy volunteers (controls). The overall prevalence of pANCAs in patients with ulcerative colitis was 70·3 per cent (71 of 101). These antibodies were still present in 29 of 39 patients after restorative proctocolectomy, in whom the median follow-up after surgery was 2 years. All five patients who had pouchitis after restorative proctocolectomy were pANCA positive. By contrast, only ten of 40 patients with Crohn's disease had pANCAs, nine of whom had Crohn's colitis. No pANCAs were detected in Controls. These results show that pANCAs are more prevalent in colonic IBD, especially ulcerative colitis. The persistence of pANCAs in the sera for 2 years after restorative proctocolectomy suggests that the antigens are not fully eradicated and, therefore, that it is not just the colon that is targeted immunologically in ulcerative colitis.