Sixteen patients with oral isoniazid, pyrazinamide, rifampin, and intramuscular streptomycin for tuberculous meningitis were studied. The concentrations of isoniazid, pyrazinamide, rifampin, and streptomycin in cerebrospinal fluid (CSF) obtained 3 hours after administration were 2.40, 34.78, 0.29, and 3.78 micrograms/ml, respectively. The CSF concentrations of isoniazid and pyrazinamide were well above the minimum inhibitory concentration for Mycobacterium tuberculosis. Concentrations of rifampin and streptomycin were above the minimal inhibitory concentration initially but declined below the minimal inhibitory concentration at later times. The CSF penetration of isoniazid, pyrazinamide, rifampin, and streptomycin was about 89%, 91%, 5%, and 20%, respectively. In eight patients who received antituberculous drugs in combination with steroids, the mean CSF and serum concentrations, as well as CSF/serum ratios at various intervals of treatment, were not statistically different (p greater than 0.05) from those of the eight patients who did not receive steroids.