Azithromycin (AZM), 10% fine granules or 100 mg capsules, were given orally to 27 children with various pediatric infections. The results of the study are shown below. 1. Pharmacokinetic investigation. We studied plasma and urinary concentrations after 100 mg AZM capsules were given. One patient received 8.3 mg/kg of AZM once a day for 3 days, and AZM concentration in plasma was 0.033 microgram/ml 48 hours after the final dosing. Doses of 8.3 and 12.5 mg/kg body weight of AZM were respectively given to two patients once daily for 3 days. As a result, AZM concentrations in urine during a period between 96 and 120 hours post-dosing were 1.67 and 4.53 micrograms/ml, respectively, and urinary excretion rate in 120 hours after the first dosing was 10.54% in the patient that was given 12.5 mg/kg. 2. Clinical investigation. Clinical efficacies were examined in 24 patients. Excellent results were obtained in 7 patients, good results in 14 patients, hence the clinical efficacy rate was 87.5%. Bacteriologically, Haemophilus influenzae strains isolates from 2 patients were eradicated in 1 and decreased in the other. Safety was evaluated in 26 patients. An adverse reaction was observed in 1 patient (urticaria). Abnormal laboratory test results were observed in 2 patients, decreased WBC in 1 and elevation of eosinophils in the other. The above results suggest that AZM is a useful oral antibiotic for pediatric patients with infection with susceptible organisms.