BACKGROUND AND OBJECTIVE: Mycobacterium tuberculosis MTB12 protein plays an essential role in pro-inflammatory responses during the early stages of human pulmonary tuberculosis (TB), even though the T-cell immunoreactivity of MTB12 is weaker than that of the 30-kDa antigen (Ag). The objective of this study was to evaluate the humoral immune responses induced by MTB12 Ag during human TB. METHODS: Using an ELISA, anti-MTB12 IgG levels in the sera of TB patients and healthy controls were compared with those induced by the 30-kDa Ag and 38-kDa Ag, or both. RESULTS: In TB patients, the sensitivity and specificity of MTB12 Ag were similar to those of other antigens at 53.0% and 95.4%, respectively. However, the sensitivity increased to 73.0% when the combination of MTB12 and 38-kDa Ag was measured. Specificity remained high when a combination of the individual antigens was used. ELISA results showed that after anti-tuberculosis treatment, the mean IgG levels against MTB12 alone or MTB12 plus 38-kDa Ag were significantly increased in the TB patients, while those against MTB12 plus 30-kDa Ag were not (P < 0.05). CONCLUSIONS: Collectively, these data suggest that MTB12, in combination with 38-kDa Ag, can be used to increase the accuracy of pulmonary TB diagnosis.