Because Streptococcus pneumoniae, Haemophilus influenzae b and Staphylococcus aureus are the major causes of bacterial pneumonia in infancy, we customarily have given a beta-lactam antibiotic and chloramphenicol as initial antibiotic therapy. Cefuroxime (75 mg/kg/day divided every 8 hours iv or im) was evaluated as single drug therapy in an open study of 100 infants and children with suspected bacterial pneumonia. The mean serum concentration of cefuroxime 30 minutes after a 15-minute infusion of 25 mg/kg iv was 29.1 micrograms/ml, and the volume of distribution was 695 ml/kg. Pleural fluid concentrations in 3 specimens were 2.2, 8.5 and 11 micrograms/ml. Median age of patients was 15 months. Bacterial etiology was established in 20 patients: H. influenzae b (8 patients); pneumococcus (8 patients); S. aureus (2 patients); Group A streptococcus (1 patient); Neisseria meningitidis B (1 patient). All organisms were susceptible to 1.25-micrograms/ml doses or less of cefuroxime. The mean number of days was 3.1 until patients became afebrile and 5.1 until respiratory symptoms were gone. Eosinophilia occurred in 10 patients. Cefuroxime is safe and effective single drug therapy for pneumonia in infants and children.