Neomycin given orally has proved to be a useful drug in controlling several forms of epidemic diarrhea of the newborn, principally that presumably due to enteropathic strains of Escherichia coli. During an epidemic period such nursery outbreaks of diarrheal illness are best controlled by administering this drug, in the dosage range of 100 mg. per kilogram per day to all susceptible infants and maintaining them on the drug for at least 6 days and possibly until the time of their discharge from the nursery.1-5 In the premature nursery this may necessitate the administration of neomycin for periods of 3 weeks or longer and raises the question of the safety of prolonged usage. This query becomes particularly pertinent in the light of recent reports indicating that many antimicrobials (e.g., sulfisoxazole, chloramphenicol, and novobiocin) cannot be administered with impunity to newborns in dosages found safe for older infants and adults.6-8