Cefpirome (HR 810, CPR), a new cephem antibiotic, was investigated for its experimental and clinical studies in pediatrics. The results obtained are summarized as follows. 1. Plasma and urinary levels of CPR were determined in 2 children (age 5 and 7 years) after the one shot intravenous injection of the drug at 20 mg/kg. Average plasma levels of the drug were 44.7 micrograms/ml, 28.5 micrograms/ml, 10.5 micrograms/ml, 4.6 micrograms/ml and 1.5 micrograms/ml at 1/2 hour, 1 hour, 2 hours, 4 hours and 6 hours, respectively, and the average half life was 1.57 hours. Average urinary levels of the drug were 1,785 micrograms/ml, 545 micrograms/ml and 198 micrograms/ml at 0-2 hours, 2-4 hours, 4-6 hours, respectively and the average urinary elimination rate was 52.0%. The results were nearly equivalent to those in adults except for urinary elimination rate which tended to be slightly lower than that in adults. 2. Cerebrospinal fluid levels in 3 cases of purulent meningitis treated with CPR were investigated. Cerebrospinal fluid levels in a case of Neisseria meningitidis were 11.5-23.1 micrograms/ml at 1 hour and 0.94 microgram/ml at 5 hours after intravenous injection of 44.4 mg/kg, 4 times a day. Cerebrospinal fluid levels in a case of Streptococcus pneumoniae were 1.01-4.23 micrograms/ml at 1 hour after intravenous injection of 49.0 mg/kg, 6 times a day, and in the other case with Streptococcus pneumoniae, the levels were 16.8-37.1 micrograms/ml at 1 hour, 11.3 and 3.60 micrograms/ml at 3 and 4 hours after intravenous injection 52.2 mg/kg, 6 times a day. These results are not inferior to those with cefotaxime or ceftriaxone. These levels appear to be higher than MIC90 values against Escherichia coli, Streptococcus agalactiae, S. pneumoniae or Haemophilus influenzae which are the major pathogens of these diseases. 3. CPR was given to 62 patients and clinical efficacy, bacteriological response and adverse reactions were evaluated. Evaluated cases for clinical efficacy included 3 cases of purulent meningitis, 1 case of acute purulent otitis media, 2 cases of acute purulent tonsillitis, 1 case of acute bronchitis, 49 cases of acute pneumoniae, 1 case of scarlet fever, 1 case of acute osteomyelitis, 1 case of acute enterocolitis, and 2 cases of acute UTI, totalling 61 cases. Clinical efficacies were excellent in 38 cases, good in 22 cases and fair in 1 case with an efficacy rete of 98.4% (excellent + good).(ABSTRACT TRUNCATED AT 400 WORDS)