Adenosine deaminase in pleural fluid (pADA), CA125 in serum (sCA125), and IFN-gamma in pleural fluid (pIFN-gamma) were measured in patients with pleurisy of various causes to evaluate their diagnostic utility in tuberculous pleuritis (TBP). We studied 39 pleural fluid samples, including 11 TBP and 28 non-TBP. With both pADA and sCA125, although the median values were much higher in TBP than in non-TBP groups, there was considerable overlap between the two groups. The sensitivity, specificity, and diagnostic efficiency were 81.8%, 89.3%, and 87.2%, respectively, when pADA values of more than 45 U ml-1 were considered, and they were 100%, 75.0%, and 84.2%, respectively, when sCA125 values of more than 35 U ml-1 were considered. In contrast, pIFN-gamma values were significantly higher in TBP patients (5.8 +/- 3.0 IU ml-1; mean +/- S.D.) than those in non-TBP patients (< 0.3 IU ml-1), leading to both a sensitivity and a specificity of 100%.