We evaluated the diagnostic performance of the Diagnos TB AG immunoassay in 171 Tanzanians with suspected pulmonary tuberculosis (TB). The sensitivity and specificity, and positive and negative predictive values of the rapid test for the detection of pulmonary TB in this population were respectively 60.0%, 33.3%, 40.3% and 52.6%. In its current configuration, this test will not help overcome difficulties in the rapid diagnosis of TB.