Evaluation of pleural fluid cholinesterase level and comparison of study of pleural fluid cholinesterase levels and serum cholinesterase levels to differentiate transudates from exudates. Light's criteria were used to compare transudate from exudate. MATERIALS AND METHODS: 56 patients of pleural effusion of different diseases like tuberculosis, malignancy, Para pneumonic effusion, congestive heart failure, nephrotic syndrome, pancreatitis were selected and studied for pleural cholinesterase levels and then serum cholinesterase levels. RESULTS: In exudates it was observed that the mean PChe and P/S Ch were higher as compared to transudates (P < 0.001).the cutoff value for PChe is taken as 2000 IU/L for the diagnosis, with this level it was found that 4 % of transudates and 0 % of exudates were misclassified. when the cutoff value of 0.50 for P/S Che ratio was used the misclassification decreased to 2 % in exudates and 2% in transudates it was observed that Using Light's criteria a sensitivity of 93 % and specificity of 85 % with positive predicative value (PP V) OF 90 % and negative predictive value (NPV) of 89 %. CONCLUSION: Estimation of pleural cholinesterase levels and ratio of pleural cholinesterase to serum cholinesterase was more efficacious and specific compared to light's criteria. Serum cholinesterase estimation is cost effective specific and more sensitive. It can be used routinely to differentiate transudates from exudates in pleural effusion of varied etiology.