The study included male and female infants delivered at University Hospital in Seattle, Washington. Women were recruited after the 28th week of pregnancy and had to be English-speaking. In addition, they planned to stay at the hospital at least 48 hours following delivery and lived in the greater Seattle metropolitan area. Infants were eligible whether they were delivered vaginally or by cesarean section. Excluded from the study were siblings of infants enrolled in the study, women who were culture-positive for gonorrhea, infants receiving systemic antimicrobials for reasons other than conjunctivitis, women receiving antimicrobials at the time of delivery, and families unlikely to be available for followup after delivery.