Fundamental and clinical evaluation on ceftriaxone (Ro 13-9904, CTRX) was performed in the field of pediatrics and the following results were obtained. The antibacterial activity of CTRX was determined against clinically isolated strains at our department. CTRX was definitely superior to CEZ and CMZ and almost equal or slightly superior to CTX in activity against Gram-negative bacteria, while the MIC of CTRX against Gram-positive bacteria was higher than that of CEZ and CMZ and about equal to that of CTX. The blood concentration of CTRX after one shot intravenous injection with 10 mg/kg was 67.98 micrograms/ml at 15 minutes, 51.96 micrograms/ml at 30 minutes, 37.51 micrograms/ml at 1 hour, 28.91 micrograms/ml at 2 hours, 20.71 micrograms/ml at 4 hours, 13.97 micrograms/ml at 6 hours and 6.45 micrograms/ml at 12 hours, while the half-life time was 3.74 hours. The blood concentration of CTRX after one shot intravenous injection with 20 mg/kg was 179.55 micrograms/ml at 15 minutes, 120.01 micrograms/ml at 30 minutes, 100.01 micrograms/ml at 1 hour, 53.75 micrograms/ml at 2 hours, 33.13 micrograms/ml at 4 hours, 26.41 micrograms/ml at 6 hours and 21.49 micrograms/ml at 12 hours, while the half-life time was 4.15 hours. The blood concentration of CTRX after intravenous drip infusion for 1 hour with 10 mg/kg was 19.54 micrograms/ml at 15 minutes, 27.19 micrograms/ml at 30 minutes, 36.57 micrograms/ml at 1 hour, 23.83 micrograms/ml at 2 hours, 19.69 micrograms/ml at 3 hours, 14.46 micrograms/ml at 5 hours, 11.02 micrograms/ml at 7 hours and 7.27 micrograms/ml at 13 hours, while the half-life time was 6.59 hours. The blood concentration of CTRX after intravenous drip infusion for 1 hour with 20 mg/kg was 61.72 micrograms/ml at 30 minutes, 108.1 micrograms/ml at 1 hour, 54.95 micrograms/ml at 2 hours, 35.68 micrograms/ml at 3 hours, 28.13 micrograms/ml at 5 hours, 20.51 micrograms/ml at 7 hours and 11.43 micrograms/ml at 13 hours, while the half-life time was 4.23 hours. There was noticed a tendency of the blood level being elevated by consecutive administration. The urinary recovery rate of CTRX ranged from 36.5 to 71.6%. The excretion rate of CTRX into the cerebrospinal fluid ranged from 5.2 to 11.6%. The excretion rate of CTRX into the pleural fluid was 31.0%. The clinical efficacy rate was 87.5% (excellent or good) in 8 children with infections treated with CTRX. The eradication of bacteria was observed in all of 5 cases bacteriologically evaluation.(ABSTRACT TRUNCATED AT 400 WORDS)