The serum-ascites albumin difference is reported to be superior to ascitic total protein, ascitic-to-serum total protein ratio, lactic dehydrogenase, and ascitic-to-serum lactic dehydrogenase ratio in differentiating between ascites from liver disease and malignant ascites, S-A greater than 1.1 reflecting portal hypertension. We analyzed ascitic fluid from 46 consecutive patients with chronic liver disease, 28 patients with ascites associated with malignancy, 10 patients with right-sided heart failure, 4 patients with hypothyroidism, and 6 patients with miscellaneous causes of ascites to determine if this albumin difference is indeed a more valuable parameter. Analysis of our data confirms with a larger number of patients that the serum-ascites albumin difference is a more reliable indicator of transudative ascites, better termed portal hypertensive ascites. Malignant ascites without liver metastases had features of nonportal hypertensive ascites, and the serum-ascites albumin difference confirms this. The characteristics of malignant ascites associated with liver metastases, however, resemble those of the portal hypertensive ascites complicating liver disease. This new parameter is also helpful in distinguishing congestive heart failure with high protein ascites and portal hypertensive ascitic features from malignant ascites without liver metastases. Of particular note, myxedematous ascitic fluid, classically categorized as exudative, had an S-A greater than 1.1, indicating the possible role of portal hypertension in the development of ascites in these patients.