Ceftriaxone is an investigational cephalosporin with a half-life of five to eight hours. In an uncontrolled study, we evaluated its efficacy and safety in 30 pediatric and 12 young adult patients with serious bacterial infections. This agent was administered to children at a dosage of 50 to 75 mg/kg/day intravenously in two divided doses. Those with CNS infections received 100 mg/kg/day. In adults, the dosage was 1 g either once or twice daily. The diseases we treated included pneumonia (17), sepsis (eight), ventriculoperitoneal shunt infections (three), osteomyelitis (three), brain abscess (two), peritonitis (two), and miscellaneous (seven). Clinical cures were achieved in all cases, although one child with cystic fibrosis and Pseudomonas pneumonia had persistent colonization in his sputum. No serious side effects were observed. Although not the agent of choice for many of these pathogens, ceftriaxone appears to represent an important alternative to therapy.