Group B streptococci and Escherichia coli are the most frequently isolated etiologic agents in neonatal septicemia. Neonatal infection that is caused by Pseudomonas aeruginosa is usually late in onset, nosocomial in origin and epidemic in pattern. However, P. aeruginosa must be considered in all neonatal infections, regardless of the age of onset, so that early, appropriate and often lifesaving antibiotic therapy may be instituted.