Background: The diagnosis of pleural effusions is sometimes difficult and needs invasive diagnostic procedures; the search for markers that will at least allow to obtain a differential diagnosis between malignant and benign effusions is the objective of many studies.Methods: The level of adenosine deaminase (ADA) and lysozyme in pleural fluid and serum was determined in 84 patients (52 with tuberculous pleural effusions – TB and 32 with malignant pleural effusions – CA), by Giusti/Galcanti and turbidimetric kinetic method.Results: In the group with TB there were significant higher serum and pleural fluid concentrations of ADA (ADAp; ADAs) and lysozyme (Lp; Ls) compared to CA. In the differential diagnosis between tuberculous and malignant pleural effusion ratios ADAp/ADAs = or > 1.8 and Lp/Ls = or > 1.5 were accepted as a cutoff level. We found significant differences between two groups in both tests (p < 0.001): in the group with TB 76.9% of patients had ADAp/ADAs ratio = or > 1.8 contrary to the group with CA where the percentage is only 9.4%. In the group with TB there were 84.6% of patients with Lp/Ls ratio = or > 1.5, contrary to the group with malignancy where the percentage is only 3.1%. ADAp/ADAs ratio of 1.8 and Lp/Ls ratio of 1.5 showed sensitivity of 76.92% and 84.65%, specificity of 80.70% and 87.71%, positive predictive value of 78.43% and 86.27%, negative predictive value of 78.83% and 86.20% and diagnostic accuracy of 78.83% and 86.23% in the diagnosis of tuberculous pleurisy, separately.Conclusions: These results suggest that the determination of the Lp/Ls and ADAp/ADAs ratios provides a simple and rapid method which can be used as a screening test in the differential diagnosis between tuberculous and malignant pleural effusions.