We evaluated soluble interleukin-2 receptors (sIL-2R), neopterin and adenosine deaminase (ADA) in pleural effusions from 93 patients with tuberculosis, malignancies, uremia, pneumonia and other kinds of pleurisy. There were significantly elevated ADA (102.7 ± 47 U/1) and sIL-2R (8,238 ± 4,117 U/ml) values in tuberculous (TB) pleural fluids as compared with other non-TB pleural fluids (p < 0.005). The neopterin levels in pleural fluid were significantly lower in the cancer group (17.3 ± 7.8 nmol/l; p < 0.005) and most strikingly elevated (309.4 ± 112.2 nmol/l; p < 0.0001) in patients with uremic pleural effusions. Using cut-off values of 60 U/l in ADA and 5,000 U/l in sIL-2R, 92.0 and 86.9% of pleural effusions were TB in origin. Eighty-four percent of patients with malignant pleural effusions had neopterin levels less than 25 nmol/l.