�

 Background & Objectives: Some special characteristics of mycobacterium tuberculosis such as long time incubation period in culture media needed for colony appearance, unavailability of serologic methods for diagnosis, along with necessity of starting treatment in the patients with severe conditions as well as isolation limitations requires the introduction of rapid and innovative diagnostic tests. On the other hand, some diagnostic tests such as Polymerase Chain Reaction (PCR) require special experimental conditions which are not easily available to clinicians. This study was designed to determine the diagnostic value of serum adenosine deaminasae in pulmonary tuberculosis and evaluate its efficacy in pulmonary tuberculosis diagnosis.

 Methods:�This cross-sectional study started in spring 2002. Continuous sampling was done and admitted patients were observed, examined and interviewed using a diagnotic test. All patients admitted with a suspected pulmonary tuberculosis diagnosis based on physical examination, history and chest X-Ray results were followed up for six months to ensure that mycobacterium tuberculosis infection was appropriately diagnosed. Blood samples were taken for serum ADA and complementary diagnostic tests. Following certain necessary tests and work-ups patients with or without tuberculosis were identified.

 Results: 131 Patients were evaluated completely. 103 had tuberculosis and 28 patients had other diseases. No statistically significant difference was found between mean level of serum ADA in two groups. But a serum level of ADA greater than 51 ^U/_L was associated with 90% positive predictive value and specificity in differentiating two groups.

 Conclusion: Serum ADA is not a suitable test for pulmonary tuberculosis diagnosis.