S-6436 or S-6437 was orally administered to 30 patients with bacterial infections including some patients with secondary infections. The following results were obtained: 21 patients had excellent effect, good 5, fair 2 and poor 2. The effectiveness was 86.7%. One gram (potency)/day of sustained release cephalexin was given to most of the patients divided into 2 doses after breakfast and dinner. This b.i.d. regimen was popular among outpatients as well. Staph. aureus isolated from 73.3% of the patients disappeared. Overall bacteriological effectiveness was 72.2%. In only 2 patients, side effects were observed. One had a mild pain in stomach and the other had aggravation of itching in complication of eczema. No abnormalities in laboratory studies which were conducted in some patients were found.