Thirty pediatric and young adult patients with bacterial meningitis were treated with ceftriaxone or "standard therapy" in a comparative trial; 41 other patients with severe bacterial infections were treated with ceftriaxone in an open protocol. Meningitis and brain abscesses were treated successfully with 50 mg/kg of ceftriaxone every 12 hours. In children, other infections were treated with 25 to 37.5 mg/kg of ceftriaxone every 12 hours. Young adults with pneumonia received 1 g of the antibiotic every 12 hours, whereas those with soft tissue infections were treated every 24 hours. All patients responded to therapy, and in all but one was the infectious process sterilized. No significant toxicity was observed. Ceftriaxone appears to be an excellent single agent for the treatment of most severe bacterial infections in pediatric and young adult patients and need not be administered more frequently than once every 12 hours.