This study is planned to evaluate the diagnostic value of TNF-$\alpha$ in serum and pleural fluid in patients with tuberculous pleurisy. 41 patients were included in the study. 18 had tuberculous effusion, 13 had parapneumonic pleurisy and empyema and 10 had malignant pleural effusion. Serum and pleural fluid TNF-$\alpha$ levels were determined by enzyme immunoassay kit (Immunotech International) in 3 groups. The mean of the ranks in serum TNF-$\alpha$ values was 21.58 in tuberculous group, 15.42 in parapneumonic group and 26.10 in malignant group and the difference between the 3 groups was not significantly different (p>0.05).The mean of the ranks in pleural fluid TNF-$\alpha$ values was 26.13 in tuberculous, 21.30 in parapneumonic and 11.35 in malignant group. The difference between the pleural fluid values of the tuberculous and parapneumonic effusion group was not significant (p>0.05) but the difference between the tuberculous and malignant group was significant (p<0.01) and also the difference between the parapneumonic and the malignant group was significant (p<0.05). The serum values were lower than pleural fluid values in tuberculous and parapneumonic effusion group. These results suggest that TNF-$\alpha$ is produced and selectively concentrated at the site of disease activity in infectious pleu-ral effusions but cannot be useful in the differential diagnosis of tuberculous and parapneumonic bacterial effusion.