Anti-endothelial antibodies (AEA) have been described in patients with rheumatoid arthritis (RA) complicated by vasculitis. In this study we made use of an ELISA and immunoblot technique (IBT) to further characterize AEA of the IgG class in serum of patients with rheumatoid vasculitis (RV) and to investigate the relationship between the presence of IgG-AEA and vasculitis. IgG-AEA as measured by ELISA or IBT could be detected in the serum from 20 of the 23 (87%) RV patients, in 2 out of 13 (15%) patients with RA and in one of 15 healthy donors. The IBT revealed reactivity of IgG-AEA against a total of 12 bands of endothelial antigens ranging in size from 16 to 68 kD. IgG-AEA as measured by ELISA and IBT in serum samples of patients followed longitudinally were present more frequently and in higher titres in patients with active RV as compared to patients with vasculitis in remission. A significant correlation was found between the presence of clinical signs of vasculitis and serum IgG-AEA reactivity against an endothelial membrane antigen of 44 kD. These data show that the pattern of IgG-AEA reactivity in the serum of RV patients is heterogeneous and suggest that IgG-AEA against one particular antigen is involved in the pathogenesis of RV.