A cooperative french trial in the treatment of pulmonary tuberculosis has compared the efficacy and the tolerance of daily antituberculous regimes, one of short duration of 18 weeks (HRSZ/HRZ), the other of standard duration of 9 months (HRE). Of 204 patients included in the trial 180 were analysed. No significant difference was found between the two regimes regarding either biological tolerance or clinical outcome. Four relapses were seen within 24 months of the onset of treatment, two in each regime, which shows that 18 weeks treatment is ethically acceptable. Such short course therapy is useful in those patients who would sometimes find prolonged therapy difficult or would be likely to abandon treatment prematurely.