Laboratory and clinical studies on biapenem (L-627), a new carbapenem antibiotic, were carried out in the field of pediatrics. 1. Antibacterial activities of L-627 against clinically isolated organisms in our department were generally high. 2. After 30 minutes intravenous infusion of L-627 at a dose of 10 mg/kg in 3 and of 12 mg/kg in 2 children, peak plasma levels of L-627 ranged from 25.6 to 44.6 micrograms/ml at the end of the infusion. The half-lives were from 0.68 to 0.94 hours. The cumulative urinary recovery rates in the first 6 hours after the start of drip infusion ranged from 11.4 to 47.5%. 3. 14 patients with various bacterial infections were treated with L-627. The clinical efficacy rate was also 92.9% and the bacteriological efficacy rate was also 92.9%. 4. No side effects were observed. A few abnormal laboratory test results were obtained, but they were mild with slight elevation of GOT/GPT and platelets in 1 each.