Tuberculoproteins A and C obtained from culture filtrate of Mycobacterium tuberculosis by alcohol fractionation were utilized in an enzyme-linked immunosorbent assay to measure the amount of reactive IgG in the sera from advanced and moderately advanced tuberculosis patients, leprosy patients and normal individuals. The A-protein detected significant levels of IgG in the sera from both advanced and moderately-advanced tuberculosis patients and patients with leprosy as compared to the normal group. Employing the C-protein, only sera from the advanced tuberculosis patients group gave significantly positive results when compared with the normal control group. The data show that the A-protein is more potent than the C-protein and has a potential serodiagnostic value.