S-6437 was orally given to 29 patients of 3 months to 12 years and 6 months of age who had respiratory or urinary tract infections. The daily dose used was 25 to 60 mg/kg divided in two doses. The following is the results of this study: 1. With 25 approximately 60 mg/kg/day, satisfactory results were obtained for upper respiratory tract infections. In lower respiratory tract infections, however, the effectiveness seemed not to be so good as that in upper respiratory tract infections. 2. Side effects such as diarrhea, loose stool, abdominal pain and eruption were observed but they were temporary. Therefore, the administration of S-6437 was not discontinued due to such side effects. 3. S-6437 was acceptable to elder children but some of children of 2 approximately 4 years of age disliked this preparation because it was not smooth in their mouths. Therefore, the preparation of S-6437 should be further improved. 4. Since it has been recognized that blood levels of cephalexin following the administration of S-6437 last for a longer period of time than regular cephalexin, S-6437 is considered to be a useful preparation. 5. B.I.D. and T.I.D. regimens of S-6437 will give clinical satisfaction to children over 6 years and ones under 6 years, respectively.