Evidence from research studies suggests a relationship between neonatal infection with Staphylococcus aureus and the level of umbilical colonization. During a 3-month prospective study (September-December 1990) the incidence and levels of S. aureus colonization were determined for all 370 live births in the Darlington Unit by taking swabs at 48 h and 8/9 days from the base of the umbilical cord. Infants were situated in one of four locations (The Special Care Unit, one of two wards or home) and the location at the time of swabbing was recorded. The overall percentages colonized at 48 h and 8/9 d were 68% and 65% respectively. Forty-eight hours after delivery, 49% showed a high level of S. aureus colonization. Although the percentage of infants colonized with S. aureus was almost identical at each sampling, only 62% were culture-positive on both occasions. Between 48 h and 8/9 days, 12% (44) of infants developed S. aureus infections of whom 35 showed heavy growth. Statistical analysis showed a significant relationship between levels of colonization at the two sampling times but no relationship between location and levels of colonization over the time period.