Patients with pleural effusions frequently present a diagnostic and therapeutic challenge, the diagnosis is based on the interpretation of the results of thoracentesis or pleural biopsy a prospective study performed on 20 patients under went different diagnostic modalities is designed to evaluate the specificity and sensitivity of the diagnostic yield of different invasive modalities used for diagnosis of chronic (oxidative) pleural effusion, these modalities include thoracentesis and subsequent pleural fluid cytology, culture and sensitivity and biochemical examination and pleural biopsy obtained either by cutting needle (Abrams’ needle), bronchoscopy or video-assisted thoracoscopy (VAT) and finally conventional surgery. All patients were subjected to thoracentesis in which it was positive only in 13 of them; nine patients were subjected to cutting needle biopsy which was positive in only 5. Bronchoscopy was done in two patients and was positive in only one of them, video-assisted thoracoscopy (VAT) was performed in 15 patients in which all the previously mentioned methods were negative and proved to be conclusive in all of them. Open pleural biopsy was done in only one patient.