To evaluate the diagnostic value of ascitic lipids to differentiate rnalignant from nonmalignant ascites, the authors studies 47 patients with ascites (22 with cirrhosis, 16 with various neoplasms and 9 with both chronic liver disease and malignancy). Ascitic fluid (AF) concentrations of cholesterol, triglycerides, phospholipids and total lipids were compared with other parameters such as AF total protein, AF to serum ratio of total protein, AF lactic dehydrogenase (LDH), AF to serum ratio of LDH, AF carcinoembryonic antigen (CEA) and AF cytology. The results were as follows: 1) The median and mean values of cholesterol, triglycerides, phospholipids and total lipids were significantly higher in malignant ascites compared to cirrhotic ascites (p<0.01). 2) The sensitivity and specificity of AF total protein in the differentiation between cirrhotic and malignant ascites were 0.75 and 0.86 respectively, AF to serum ratio of total protein (0.69 and 0.91), AF LDH (0.56 and 0.91), AF to serum ratio of LDH (0.63 and 0.86), AF CEA (0.56 and 1.00), and AF cytology (0.56 and 1.00). 3) The best discrimination value of cholesterol was 42 mg/dl. AF cholesterol concentration overlapped the least and showed the highest sensitivity (0.88) and specificity (1.00). 4) There was no significant difference between patients with cirrhosis and both chronic liver disease and malignancy in the AF concentration of cholesterol, triglycerides, phospholipids and total lipids. 5) Significantly positive correlations were found between cholesterol/total protein (r=0.83, p<0. 001), cholesterol/phospholipids (r=0.93, p<0.001), cholesterol/triglycerides (r=0,54, p<0.001) and cholesterol/total lipids (r=0.81, p<0.001). In conclusion, AF lipids, especially AF cholesterol concentration, were parameters valuable for the differential diagnosis of ascites.