Laboratory and clinical studies were performed as follows on cefminox (CMNX, MT-141), a new cephamycin antibiotic. Pharmacokinetics Serum concentrations of CMNX were measured in 4 patients given CMNX for prophylactic purpose during cardiac catheterization. In 2 patients given 20 mg/kg of CMNX by intravenous bolus injection, the average of peak serum concentration was 178.9 micrograms/ml at 15 minutes. The mean urinary recoveries in these 2 cases was 66.9% within 6 hours after injection. In 2 patients given 20 mg/kg of this drug by 1 hour drip infusion, the peak serum concentration was obtained at the time drip was completed, and the average value was 68.3 micrograms/ml. Clinical efficacy CMNX was administrated intravenously to 13 patients in dose of 52.9 approximately 96.0 mg/kg t.i.d. or q.i.d. for 4 approximately 7 days; 3 with tonsillitis, 6 with bronchitis, 1 with bronchopneumonia, 1 with UTI, 1 with lymphadenitis and 1 with enterocolitis. The overall efficacy rate was 92.3%, i.e., efficacy was excellent in 12, and poor in 1. Bacteriological efficacy was excellent, i.e., 3 of 3 strains disappeared. Side effects were observed in 3 cases, i.e., 1 case of eruption, 1 case of diarrhea and 1 case of transient eosinophilia. The above results suggest that CMNX is a useful antibiotic for treating pediatric bacterial infections.