Because of the difficulty in isolating the causative organism, pericardial tuberculosis is rarely, diagnosed Adenosine deaminase activity measured in the pericardial fluid of 108 patients was initially of undetermined origin. Subsequently we classified five sources: (1) tuberculosis (20 cases); (2) idiopathy (82 cases), (3) neoplasia (three cases); (4) purulent bacterial infection (two cases); and (5) radiotherapy (one case). The highest mean adenosine deaminase value (126 +/- 16.68 U. l(-1)) was found in group 1; other values were 29.4 +/- 8.9, 27 +/- 7.21, 29.5 +/- 13.4, 26 U. l(-1) in the idiopathy neoplasia, purulent bacterial infection and radiotherapy groups, respectively. There was a statistically significant difference between group 1 and the other groups (P less than 0.001), indicating that the adenosine deaminase value has 100% sensitivity and 91% specificity. In addition, there was a positive correlation between high adenosine deaminase values and the development of constrictive pericarditis. In this study, two patients required pericardectomy. Therefore, the adenosine deaminase value is a significant prognostic indicator for the development of constrictive pericarditis in tuberculous pericarditis.