Viral infections of the mesenteric microvascular endothelium have been hypothesized as pathogenetic factors in inflammatory bowel diseases. The aim of this study was to determine whether immunoglobulin M (IgM) antibody against measles virus is associated with disease. The IgM antibody was detected by indirect antibody test in 36 patients with evidence of Crohn's disease (23 males and 13 females, median age 40 years, range 20-66), 22 patients with ulcerative colitis (14 males and 8 females, median age 42 years; range 19-65), 59 patients with a chronic active hepatitis (35 males and 24 females, median age 56 years, range 38-77) and 30 blood donors (20 males and 10 females, median age 45 years, range 29-62). Twenty-eight of 36 patients (78%) with Crohn's disease and 13 of 22 patients (59%) with ulcerative colitis tested positive as compared to only 3 of 89 (3.3%) controls (P < or = 0.001). The detection of IgM anti-measles virus in the majority of patients with Crohn's disease and in about half of ulcerative colitis patients as compared to a very low prevalence in patients with other chronic inflammatory disease is consistent with the hypothesis that the measles virus has pathogenetic implications in inflammatory bowel diseases.