Perinuclear anti-neutrophil cytoplasmicantibodies (P-ANCA) of the IgG class have been reportedin inflammatory bowel disease, mainly in ulcerativecolitis. Since this disease affects the gastrointestinal tract, we determined whether IgA class ANCAwere present in inflammatory bowel disease. We used anindirect immunofluorescence assay for IgG and IgA ANCAtesting. Sera from 34 patients with Crohn's disease and 29 patients with ulcerative colitis werecollected together with clinical and laboratory data. Wefound IgA class ANCA of a perinuclear type in 52% ofpatients with ulcerative colitis and in 9% of Crohn's disease patients. There was a significantassociation between the presence of IgA ANCA and theoccurrence of blood in the feces in the ulcerativecolitis group (P = 0.03). IgG ANCA was found in 56% ofpatients with ulcerative colitis and in 7% of patientswith Crohn's disease. Because of partial overlap betweenIgG and IgA ANCA positivity, the sensitivity of ANCAtesting in ulcerative colitis increased from 56% up to 78% by combining IgG and IgA assays. Inconclusion, IgA ANCA occurs with a high prevalence inulcerative colitis. Moreover there is a possiblerelationship between IgA ANCA and disease activity in ulcerative colitis.