The aim of this study was to test the diagnostic value of ascitic fluid cholesterol and triglycerides concentrations and of serum-ascites albumin concentration gradient in the differentiation between cirrhotic and malignant ascites. These biological parameters were determined, on the one hand in 34 cirrhotic patients, 6 of them having an hepatocellular carcinoma and 6 others having a spontaneous bacterial peritonitis and, on the other hand, in 16 patients with malignant ascites, 13 of them having an abdominal extra-hepatic or pelvic cancer, and 3 others having an extra-abdominal cancer with multiple liver metastases. Ascitic carcinoembryonic antigen assay and ascitic fluid cytology were also done in the 50 patients. In differentiating the cirrhotic patients from those with malignancy, ascitic fluid cholesterol concentration (discriminating value less than 1.1 mmol/l) ascitic fluid triglycerides concentration (discriminating value 0.5 mmol/l) and serum-ascites albumin concentration gradient (discriminating value greater than 11 g/l) allowed a diagnostic efficiency of 0.92, 0.80 and 0.77, respectively. Ascitic fluid cytology showed presence of malignant cells in 3/6 patients with hepatocellular carcinoma associated with cirrhosis, in 9/16 patients having a malignant ascites, and was negative in other patients. Ascitic carcinoembryonic antigen assay was abnormal only in 3/16 patients with malignant ascites. These results suggest that measurement of ascitic fluid cholesterol concentration must be included in the initial evaluation of patients with ascites of unknown origin.