In this study, serum and ascites total protein, albumin, lactate dehydrogenase, alkaline phosphatase, gamma-glutamyl-transpeptidase enzyme activities, and serum and plasma fibronectin levels were determined in patients with cirrhosis (n = 39) and in those with different types of malignancies (n = 23). In malignant ascites, ascitic fluid protein levels were increased 3.3 times when compared with the levels in the cirrhotic ascites. The levels of the ascitic fluid lactate dehydrogenase compared with the serum levels were found to be significantly different (p < 0.001). In cirrhotic and malignant ascites, alkaline phosphatase values were 21 +/- 16 units/liter and 75 +/- 71 units/liter, respectively (p < 0.001). Fibronectin concentrations of the patients with malignancy were increased 2 times as compared with those of cirrhotic patients (p < 0.001). The correlations between ascitic fluid fibronectin levels and total protein levels were found to be moderately significant. These results suggest that fibronectin levels together with the protein levels, lactate dehydrogenase, alkaline phosphatase, and gamma-glutamyl-transpeptidase enzyme activities may be used for the differential diagnosis of ascites.