Pediatric patients with serious infections are usually hospitalized for parenteral antibiotic treatment. We studied prospectively 74 pediatric patients with community-acquired serious infections and used once daily intramuscular ceftriaxone. Seventeen patients (23%) were initially hospitalized and 57 (77%) patients were treated entirely as outpatients. An initial intramuscular dose of 75 mg/kg was followed by daily doses of 50 mg/kg (maximum, 1.5 g). Infections treated included periorbital/buccal cellulitis, other cellulitis, urinary tract infections, pneumonia, osteomyelitis, mastoiditis, suppurative arthritis and orbital cellulitis. Organisms were recovered from cultures of 37 (50%) patients and 6 (8%) patients were bacteremic. Bacteria included Gram-positive (mostly Staphylococcus aureus) and Gram-negative (mostly enteric bacilli and Haemophilus influenzae organisms). No serious side effects were observed. Of 74 patients 72 (97%) were cured and improvement was usually observed within 24 hours. Two patients did not improve: one with chronic Pseudomonas mastoiditis; and one with lung abscess. Based on previous experience it is estimated that 376 hospitalization days were saved. All 72 successfully treated patients and their parents resumed normal activity within 72 hours of starting therapy. Our data suggest that ceftriaxone can be used for outpatient treatment of some infectious diseases.