The approach to the study of the patient with ascites should include biochemical and cytologic analysis of the ascites. The albumin ascites serum gradient and total proteins separate the ascites ascites caused by portal hypertension from the neoplastic ascites and peritoneal tuberculosis. Other parameters are the measurement of fibronectin and cholesterol, both of them with the cytology make the diagnosis of malignant ascites. More than 250 leukocytes per mm3 in the ascites, predominantly lymphocytes, peritoneal tuberculosis can be the cause. In conclusion the ascites analysis is the first election procedure for the study of the cause of ascites.