Introduction: Adenosine deaminase (ADA) is one of the major enzymes in purine metabolism. There are 2 isoforms of ADA: ADA1 and ADA2. The principal action of this enzyme is in immune system cells, the level of ADA in T-cell is 5-20 fold more than B-cell. The level of ADA elevates as the lymphocyte (T-cell) activity increase. Tuberculosis has been studied extensively with relevance of ADA levels and apart from serum, various body fluids as pleural, peritoneal, cerebrospinal fluids of patients of Pleural effusion, Ascitis and Tubercular Meningitis, has also its raised levels. Measurement of the level of (ADA) enzyme in body fluids is a helpful diagnostic tool. Aim: To study the serum Adenosine Deaminase Activity in patients of Pulmonary Tuberculosis and to evaluate the diagnostic significance of ADA activity in serum in these patients. Material and Methods: Present study was carried out in fifty patients of both the sexes with different ages suffering from Pulmonary Tuberculosis attending OPD and admitted in Medicine Wards in Pt. J.N.M.Medical College Hospital, Raipur C.G. 20 normal healthy individuals were included as control subjects. The diagnosis of Pulmonary Tuberculosis was established by clinical history, physical examination, suggestive radiological changes and presence of AFB on sputum smear examination. Sputum positivity is taken as diagnostic of Pulmonary Tuberculosis however sputum negative cases with suggestive radiological signs were also included in the study. Estimation of serum ADA of study and control groups was done by Galanti and Guisti methods by Spectrocolorimeter in Biochemistry Lab. Results: 50 cases of different types of pulmonary tuberculosis and 20 controls were studied for serum ADA levels. The mean serum ADA level in controls was 9.88 ± 0.47 U/L which was taken as the base line values. The mean serum ADA level in study group was 36.74 ± 2.83 U/L which is highly significant (p< 0.001). These values are significantly higher than the corresponding value obtained in the control group. Mean serum ADA levels in sputum positive cases was 38.32 U/L and in negative cases was 35.99 U/L. In Group I Infiltrative lesions 22 cases and mean serum ADA levels was 35.95 ± 3.051 U/L. Group II of Fibrocavitary tuberculosis 21 cases and mean serum ADA levels was 37.96 ± 2.167 U/L. Group III Tubercular consolidation there were 7 cases and mean serum ADA levels was 35.70 ± 3.009 U/L. Significantly higher serum ADA level (p< .001) was observed in each group as compared to controls. Radiologically in Group I minimal disease 20 cases and mean serum ADA level was 35.76 ± 3.109 U/L. Group II moderate advance disease 23 cases and mean serum ADA level was 37.07 ± 2.624 U/L. Group III far advance disease 7 cases and mean serum ADA levels was 38.45 ± 1.643 U/L. We observed that all radiologically positive cases of pulmonary tuberculosis had significantly (p <.001) higher serum ADA level as compared to control. Conclusions: There was no variation in the serum ADA levels of pulmonary Tuberculosis cases belonging to various age groups and either sex. In present study significantly higher values of serum ADA level was observed in presence of illness more than one month duration. It was raised significantly in both sputum positive as well as negative cases. ADA was raised significantly in all clinical groups of pulmonary Tuberculosis. It was observed that ADA was raised significantly in different radiological extent of disease. It was concluded that the serum ADA level estimation is a reliable and specific diagnostic test in various forms of Pulmonary Tuberculosis.