The authors present the results obtained with rifampycin, a new rifamycin derivative, in the treaiment of 31 cases of bacterial injections; in 25 of them the isolation of the probable infections agent ivas performed. Rifampycin was given in the daily dosage of 20 mg/kg of body weight for children and 450 to 900 mg for adults at 12 hours intervals. Treatment was given for 4 to 15 days according to the case. All the patients loere submitted to careful clinical and laboratorial investigations before, during and after treatment in order to detect any important reaction related to the drug. Results were considered very good in general, no side-effects being observed due to the therapy.