In this work we look for the antibody response to M. tuberculosis antigens in 38 children with pulmonary tuberculosis: 18 bacteriologically and 20 clinically diagnosed as compared to the response of 52 children with other respiratory illnesses in which tuberculosis was definitively ruled out. In this control group 24 had been BCG vaccinated and 28 had not. Antibodies were detected by ELISA and immunoblot using a crude extract of M. tuberculosis as antigen. All 38 tuberculous diagnosed children tested positive, by ELISA, to the bacterial extract as did previously vaccinated controls (18/24), while all 28 non vaccinated controls gave negative results (sensitivity = 1.0, specificity = 0.68). By Western blot, tuberculous patients recognized a 12 kDa protein that was not recognized by the control vaccinated group. This partially purified protein which was used in an ELISA resulted positive in all 18 bacteriologically, in 17/20 clinically diagnosed patients, and in only 6/24 vaccinated controls. Specificity increased to 0.86, with a sensitivity of 0.93.