Cefadroxil was administered at a daily dose of 50 mg/kg in 113 children including acute respiratory tract infections suspected to be a bacterial infection and other febrile diseases. Among 41 cases in which pharyngeal culture was made twice before and after administration or urine and feces cultures were made, 20 cases (48.8%) were good bacteriologically, 5 cases (12.2%) were poor, and 16 cases (39.0%) were unknown. Clinical efficacy was obtained in 105 cases (92.9%) out of 113 cases. Microbial substitution was noticed in 12 cases (29.3%) out of the cases of which pharyngeal culture was made after cefadroxil administration. Haemophilus influenzae was detected newly after the administration in 7 cases (58.3%) out of these 12 cases. Bacteriological efficacy was obtained in 5 cases of acute respiratory tract infection of which pathogen was considered to be Haemophilus influenzae. No microbial substitution was noticed in these 5 cases. As to the side effects of cefadroxil administration, only a slight diarrhea was observed in 2 cases.