Concentrations of pyrazinamide were measured in serum and cerebrospinal fluid (CSF) of 17 adult patients with tuberculous meningitis up to six months after starting treatment. Pyrazinamide penetrated excellently into the CSF and mean concentrations at various intervals up to six months of treatment were consistently above that required for inhibition of the growth of Mycobacterium tuberculosis. The blood/CSF partitioning of pyrazinamide does not change as the patients recover from the meningitis.