The value of adenosine deaminase activity (ADA) in ascitic fluid was examined in 12 patients with confirmed peritoneal tuberculosis and compared with that of 96 patients with ascites of other different etiologies as an age-matched control group, to determine the diagnostic value of the ADA activity in tuberculous ascites. The mean adenosine deaminase activity (ADA) value in ascitic fluid of the tuberculous peritonitis group was 47.9 +/- 21.9 IU/L and in the control group 9.6 +/- 5 U/L (mean +/- SD); p less than 0.01. A different method than that usually reported in tuberculous peritonitis was used for ascites ADA estimation. The best sensitivity and specificity was obtained when greater than 32 U/L was used as a cutoff point. The ascites ADA activity correlated with the ascites total protein concentration in the tuberculosis group (r = 0.842). Our findings confirm other results and support the ADA activity determination in ascitic fluid as a useful noninvasive screening test in the diagnosis of peritoneal tuberculosis in endemic areas or in high risk patients. However, false-negative results may occur in those patients in which ascites total protein concentration is low.