A patient with rheumatoid arthritis (RA) experienced great improvement in her RA when given antituberculous treatment for pulmonary tuberculosis (TB). Two of the drugs used in TB, rifampicin and isoniazid, include immunomodulatory effects among their properties. To investigate whether these drugs have any effect in RA, we studied 20 patients who were given either rifampicin 600 mg daily (10 patients) or rifampicin 600 mg with isoniazid 300 mg daily (10 patients). Eighteen patients completed at least 3 months' treatment. Six of the 7 patients with early RA (less than 3 years) improved; their median erythrocyte sedimentation rate fell from 43.5-10 mm/h (p = 0.036) and median serum C-reactive protein from 40-0 mg/l (p = 0.036). Eleven patients with longer histories of RA did not improve. Our results suggest rifampicin with or without isoniazid may be effective in RA.