In this study, we detected circulating antibodies to crude surface antigens isolated from cultured human dermal microvascular endothelial cells(HDMEC) and HMEC-1 in the sera of Beh?et's disease. Also, we evaluated the usefulness of isolated crude surface antigens from HDMEC and HMEC-1 as an antigen for the detection of antiendothelial cell antibody in sera from patients with Beh?et's disease. IgM antibody reacted with the HDMEC surface protein in 63.2% of sera from patients with Beh?et's disease. In systemic lupus erythematosus(SLE), both IgG(52.5%) and IgM antibodies(72.5%) reacted with endothelial cell surface proteins. The same results were obtained in enzyme-linked immunosorbent assay using HMEC-1 surface protein as an antigen. IgM antibody levels were elevated in sera of patients with Beh?et's disease showing reactive circulating immune complex. The percentage of thrombophlebitis was higher in the IgM-positive group compared to the IgM-negative group. Beh?et's disease serum containing anti-endothelial cell IgM antibody reacted with the 44kDa protein of both HDMEC and HMEC-1 in Western blotting. In dot blotting using the 44kDa HDMEC surface protein, IgM-positive sera of SLE patients and normal controls did not react with the protein, but only IgM-positive sera from Beh?et's disease patients reacted with the protein. The results indicate that anti-endothelial cell IgM antibodies reacted with the surface protein isolated from cultured HDMEC in the sera of patients with Beh?et's disease, and these antibodies may be disease-specific antibodies for Beh?et's disease. In addition, these results show that the crude surface antigens isolated from cultured HDMEC and HMEC-1 can be utilized for the detection of antiendothelial cell antibodies in Beh?et's disease.