Objective: To investigate the diagnostic significance of biochemical markers and pentraxin-3 in the differential diagnosis of pleural effusions. Methods: The prospective clinical study was conducted at the Suleyman Demirel University, Isparta, Turkey, from January 2013 to June 2014, and comprised patients with pleural effusion. Pleural effusions were tested for glucose, protein, lactate dehydrogenase, and pentraxin-3 while simultaneous C-reactive protein and white blood cell levels were studied in the serums. Data was analysed using SPSS 22. Results: Of the 96 patients, 48(50%) had malignant disease, 33(34%) had benign pleural effusion, and 15(16%) had empyema. In terms of glucose, protein, lactate dehydrogenase in the pleural effusions and C-reactive protein values in serums, significant differences were observed among the three groups (p<0.05). The pentraxin-3 levels in the empyema group was significantly higher than in the benign cases (p<0.033). No significant difference was observed in terms of the other variables between the groups (p>0.05). Conclusions: Serum C-reactive protein and pentraxin-3 levels were not found to be individually conclusive in the differential diagnosis of pleural effusion. Also, lactate dehydrogenase levels were higher and glucose levels were lower in empyema.