Infection of the newborn infant with Group B hemolytic streptococcus is increasing in importance as other pathogens decline. Such infection may appear within the first 48 hours of life and resemble respiratory distress syndrome, or around the tenth day, when signs of meningeal irritation may be present. Early onset disease may be due to any of the five serotypes of the Group B streptococcus and is fatal in a high percentage of cases. Late onset infection usually is due to serotype III. The epidemiologic aspects of early and late infection appear to differ, and a nosocomial source may be involved in the latter. Penicillin prophylaxis may be useful.