Department of Internal Medicine, “Sotiria” General Hospital of Athens Measurement of ascitic fluid adenosine deaminase (ADA) and serum cancer antigen 125 (CA 125) may represent an effective tool in the prompt diagnosis of tuberculous peritonitis. We report the case of an immunocompetent male adult where diagnosis was made on the basis of increased values of ascitic ADA and serum CA 125. Immediate initiation of antituberculous treatment resulted in quick resolution of ascites. Diagnosis was confirmed six weeks later with positive cultures of bronchoalveolar lavage for Mycobacterium tuberculosis. ADA and CA 125 should be considered as rapid, noninvasive diagnostic tests for tuberculous peritonitis. Pneumon 2005, 18(2):223-227.