Fundamental and clinical trials were carried out with cefminox (CMNX, MT-141) in pediatric infections. Results were as follows. The mean serum concentrations of CMNX following intravenous injection of 10, 20 and 40 mg/kg were 73.1, 112.5 and 181.4 micrograms/ml at 15 minutes after injection, respectively. The serum half-life times were 1.37, 1.20 and 1.53 hours, respectively. Average recovery rates in the urine until 6 hours from the start of injection were 91.4, 59.4 and 85.8%, respectively. The antimicrobial activity of CMNX against clinically isolated organisms was measured; CMNX was more active than CMZ and CEZ against H. influenzae. CMNX was equal to or more active than CMZ and CEZ against E. coli. CMNX was administered clinically to 32 pediatric patients with various infections; 19-pneumonia, 5-bronchopneumonia, 3-bronchitis and 5-pyelonephritis. Overall efficacy rate was 93.8%. Slight elevation of S-GOT and S-GPT was observed in 2 patients. No other serious side effect was observed.