The neurological manifestations and toxicities of 12 antituberculosis drugs [isoniazid, rifampicin (rifampin), ethambutol, p-aminosalicylic acid, pyrazinamide, streptomycin, kanamycin, ethionamide, cycloserine, capreomycin, viomycin and thiacetazone] are reviewed. Their effects upon the central nervous system, cranial nerves, peripheral nerves and the neuromuscular junction are examined, and drug interactions of neurological concern are briefly discussed. Isoniazid is well known to increase the concentrations of gamma-aminobutyric acid in neural tissues. Although conflicting data have been published, isoniazid may play a limited future role in reducing the degree of adventitious movements noted in certain neurological diseases such as multiple sclerosis, spasmodic torticollis, and other segmental dystonic syndromes. With rifampicin neurological complications have been observed infrequently. Rifampicin penetrates into the CSF and has been shown to have useful activity against various micro-organisms in the CSF, including certain viruses; however, contrary to earlier suggestions, it appears to have no role in the treatment of subacute sclerosing panencephalitis. A number of studies have indicated that isoniazid is associated with a large number of accidental and intentional poisonings. The highest incidence has been observed with Southwestern American Indians in which this agent was involved in 7% of all suicide attempts and 19% of the suicide deaths. Degeneration of the optic chiasma and nerve is a well-known adverse effect of ethambutol; toxicity is manifested by impairment of visual acuity, marked loss of colour discrimination, constricted visual fields, and central and peripheral scotoma. Ototoxicity is a well known problem caused by streptomycin, kanamycin, capreomycin and viomycin. The use of streptomycin in pregnant mothers is associated with congenital deafness in newborns in certain cases. The aminoglycoside antibiotics are also associated with flaccid paralysis following neuromuscular blockade. Adverse reactions to cycloserine are mainly dose-related with neurological and psychiatric syndromes noted in up to 50% of patients. Recent data indicate that isoniazid, rifampicin, ethambutol, pyrazinamide, streptomycin, kanamycin, ethionamide, and cycloserine appear in measurable quantities in the cerebrospinal fluid. Five of these compounds (isoniazid, rifampicin, ethambutol, kanamycin, cycloserine) pass to some degree through non-inflamed meninges. Other than discontinuation of the therapeutic regimen and general supportive measures, very few methods are described in the literature for treatment of acute intoxications with antituberculosis drugs.