Antibodies reactive with cytoplasmic components of neutrophils (ANCA) have received much attention because of their association with vasculitis and other inflammatory disorders. In this study, ELISA and immunofluorescence assays were employed to detect antimonocyte-specific antibodies and similar assays were used in parallel to detect anti-neutrophil cytoplasmic antibodies in a range of patient sera: Wegener's granulomatosis (14), Crohn's disease (46), ulcerative colitis (43), sarcoidosis (40), rheumatoid factor positive (15), and normal controls (22). Using an ELISA, anti-monocyte antibodies were detected in (figures in parentheses represent anti-neutrophil results): Wegener's granulomatosis, 79% (93%); sarcoidosis, 30% (5%); Crohn's disease, 20% (11%); ulcerative colitis, 0% (49%); rheumatoid factor-positive sera, 0% (0%). Excellent concordance (>98%) was found between the ELISA and immunofluorescence assays and all of the anti-monocyte antibodies gave a cytoplasmic pattern of staining. This is the first report demonstrating the presence of antibodies specific to the cytoplasmic components of monocytes in patients with granulomatous disease and these findings enhance our understanding of auto-antibody responses against phagocytic cell components.