This research was carried out to differentiate pleural effusions due to tuberculosis from those due to other causes, malignancies according to the pleural fluid and plasma adenosine deaminase (ADA) levels. A total of 132 patients who had pleural effusions were included in the present study. Patients were divided into eight groups according to the etiology. Of those 132 patients, 30 had tuberculosis, 28 had non specific empyema, 4 had tuberculous empyema, 30 had malignant neoplastic disease, 10 had thromboembolic pulmonary disease, 10 had pleuropneumonia, 10 had congestive heart failure and 10 had non specific pleurisy. Venous blood and pleural fluid samples were obtained for ADA determination. The results were expressed as mean±SD. The Kruskal-Wallis Anova and Mann Whitney tests were used to analyze the data for statistical significance. Patients with tuberculous empyema and non-specific empyema had significantly higher mean serum ADA activity than the other groups (p0.05). The mean (±SD) ADA concentrations in pleural fluid were: 36.6±16.2 IU/L in tuberculosis pleurisy; 59.8±22.6 IU/L in non specific empyema; 89.6±21 IU/l in tuberculous empyema. These results were found to be statistically significant when compared with the other groups (p