Twenty five children were treated with rokitamycin (RKM) and its clinical efficacy and side effects were evaluated. Ages of the patients ranged from 13 days to 10 years. Doses of RKM ranged 17.1-39.3 mg/kg/day for 2.3 to 17.7 days. Twenty four patients including 8 Mycoplasma pneumonia, 5 bronchopneumonia, 6 bronchitis, 2 streptococcosis, 1 otitis media, 1 tonsillitis and 1 Chlamydia conjunctivitis were evaluated for clinical efficacy. Results were excellent in 7, good in 12, fair in 4, and poor in 1 patient. One patient was excluded from the evaluation, because the patient was treated with erythromycin before entering this study. Out of the 25 patients, 3 cases showed eosinophilia, 2 cases showed elevated GOT and GPT but no adverse clinical signs due to RKM were observed. The pharmacokinetics of RKM was studied in 5 patients whose ages ranged from 8 to 12 years. Plasma peak concentrations of RKM in 2 patients were 0.14 and 0.16 micrograms/ml at 30 minutes after doses of 5 mg/kg. Peak concentrations in 3 patients ranged from 0.32 to 1.02 micrograms/ml after doses of 10 mg/kg. Portions of the drug excreted into urine within 6 hours were 0.49 and 1.03% in 2 patients each of whom was given doses of 5 mg/kg, and ranged from 1.16 to 1.30% in 3 patients, each given 10 mg/kg. Metabolic products in urine within 4 hours after doses of 5 to 10 mg/kg were studied in 4 patients. Leucomycin A7 and leucomycin V accounted for almost 90% of all the related compounds excreted.