Paracentesis is a technique used to remove excess peritoneal fluid (ascetic fluid) from the abdominal cavity. It has a diagnostic and therapeutic role. A sample of the fluid is analyzed and the cause of the ascites may be determined. It is less effective than a biopsy in diagnosing peritoneal mesothelioma as some cells may appear benign. The fluid is drained through a large bore needle inserted in the peritoneum.