Abstract: The levels of NO were determined in pleural fluid and serum from 24 patients with tuberculous pleurisy and 49 nontuberculous (28 cases of malignant, 2l cases of transudative). There were significantly elevated NO values in tuberculous pleural fluid as compared with malignant effusi0n. A significantpositive correlation was observed between NO levels and IL-2R levels in tubercul0us pleural fluid (Y =0.654, P 0.01)- Fixing the cut off point of NO values at l5OUmol/L the tuberculous pleural effusi0n caseswere differentiated from the nontuberculous with a sensitivity, specificity value and accuracy 0f over 80 percent.