The levels of IgG and IgM antibodies were evaluated in 60 patients with pulmonary tuberculosis, who were compared with a group of 30 tuberculin-negative healthy controls and another group of 10 healthy tuberculin-positive individuals. The technique for the quantification of antibodies against M. tuberculosis was an enzyme immunoassay, using purified tuberculin as antigen. The mean (means) IgG and IgM values and their standard deviations (SD), expressed in optical density units, were as follows: for the tuberculin-negative control group: IgG 0.029 +/- 0.013, IgM 0.032 +/- 0.010; for the tuberculin-positive control group: IgG 0.023 +/- 0.007, IgM 0.033 +/- 0.012; and for the group of patients: IgG 0.054 +/- 0.016, IgM 0.051 +/- 0.017. Fifty per cent of patients (30) were positive for IgG, 46.6% (28) were positive for IgM and 28.3% (17) were positive for both immunoglobulins. Those values higher than the mean of control group plus two SD were considered as positive. In the group of tuberculous patients a significant increase of IgG was observed, which was more marked after two weeks of antituberculous chemotherapy in patients with prolonged course. There appears to be a good correlation between the levels of immunoglobulins and the clinical status.