Management of tuberculosis in a hospital environment is well systematized and may include chemoprophylaxis, which may be hazardous when used in psychiatric impairments. We examined retrospectively adverse events occurring during a 6-month period of antituberculosis treatment. Besides patients initially treated for active pulmonary tuberculosis, 16 other patients have benefited from chemoprophylaxis with isoniazid (INH) and/or rifampicin (RFP). All these patients (mean age 53 years) had been institutionalized for several years. Fifteen of them still received a mean of 5.4 +/- 2.2 drugs including 3.3 +/- 1.4 psychotropic agents. During antituberculous treatment, 5 patients (29 per cent) presented side effects: hyperuricaemia with pyrazinamide, neutropenia, dysphagia and anorexia, dizziness and falls, diabetes and fatal fulminant hepatitis associated with INH. Drug interactions were systemically searched for. Three probably led to clinical manifestations: they implicated INH with carbamazepine, RFP with theophylline and RFP with haloperidol. Our results suggest a greater sensitivity for adverse effects and drug interactions in psychiatric institutionalized patients. They pose the problem of the appropriateness of antituberculous chemoprophylaxis in such patients, particularly because of communication difficulties and polytherapy. The INH-RFP regimen should be avoided and the clinical and biological follow-up reinforced.