Preclinical studies were carried out on cefotetan (CTT), together with clinical studies in the field of pediatrics. The following results were obtained. A total of 114 clinical isolates that have been stored in the authors' department was employed to determine the minimum inhibitory concentrations (MICs) of CTT against various bacterial species. Against E. coli, Salmonella, K. pneumoniae and P. mirabilis, the MICs of CTT showed a peak at 0.78 micrograms/ml, and most of the strains were inhibited by a CTT concentration of 6.25 micrograms/ml or less. The MICs for S. marcescens strains showed a peak at 25 micrograms/ml, with 25% of the strains having MICs of 3.13 micrograms/ml or less, and 67% having MICs of 25 micrograms/ml or more. All of the P. aeruginosa strains had MICs of over 100 micrograms/ml. Against all of the tested strains of S. aureus, a Gram-positive bacterium, CTT showed MICs of 12.5 micrograms/ml or more, while all of the strains of S. faecalis were found to have MICs of over 100 micrograms/ml. CTT was administered intravenously to pediatric patients as a bolus injection, and then the concentration of the antibiotic in the serum was determined as a function of time. When the dosage rate was 10 mg/kg, the mean serum levels were as follows; 58.2 micrograms/ml at 30 minutes, 45.5 micrograms/ml at 1 hour, 33.6 micrograms/ml at 2 hours, 18.0 micrograms/ml at 4 hours and 11.7 micrograms/ml at 6 hours after the injection. The half-life of CTT in the serum at this dosage was thus 2.40 hours. Similarly, at a dosage rate of 20 mg/kg, the mean values at the various times were; 98.6 micrograms/ml at 30 minutes, 75.6 micrograms/ml at 1 hour, 57.8 micrograms/ml at 2 hours, 35.5 micrograms/ml at 4 hours and 23.2 micrograms/ml at 6 hours subsequent to the injection. The half-life of CTT in the serum in these cases was 2.73 hours. CTT was drip-infused intravenously over a period of 1 hour, and then the serum concentration of the drug was monitored with the passage of time. Subsequent to the administration of 10 mg/kg, the mean serum concentrations were as follows; 48.8 micrograms/ml at 30 minutes, 81.5 micrograms/ml at 1 hour, 42.2 micrograms/ml at 2 hours, 23.6 micrograms/ml at 4 hours and 14.8 micrograms/ml at 6 hours subsequent to the injection. The half-life of CTT in the serum after this intravenous drip infusion was thus 2.13 hours.(ABSTRACT TRUNCATED AT 400 WORDS)