Production of interferon (IFN)-alpha and IFN-gamma were examined in 31 patients with acute tuberculosis, 12 patients with atypical mycobacterial disease. IFN production was examined in cultures of unseparated fresh whole blood. Production of IFN-alpha was induced by hemagglutinating virus of Japan and production of IFN-gamma was induced by PHA. Patients with mycobacterial disease produced significantly less IFN-alpha than healthy subjects. In patients with acute tuberculosis, effective chemotherapy for 2 months restored IFN-alpha production. Patients produced less IFN-gamma than healthy subjects, but the difference was not significant. Patients with high serum CRP levels tended to produce little IFN-alpha. These results suggest that measurement of IFN production is useful for immunological evaluation of patients with mycobacterial disease.