The mean CSF ADA activity was found to be significantly higher in CSF of TBM patients, 14.31 ± 3.87 (2.99–26.94), mean ± SD with range, than in the CSF from non-TBM infectious meningitis, 9.25 ± 2.14 (4.99–13.96) and from the non-infectious neurological disorders group, 2.71 ± 1.96 (0.00–7.68), P < 0.0001 for both comparisons. The gene discussed is ADA; the disease is meningeal tuberculosis.