An analysis was made of all cases of bacteraemia that had occurred in the referral neonatal intensive care unit at Hammersmith Hospital during the years 1976--79. One hundred and thirteen infants had positive blood cultures; 27 were born in the hospital, and 86 admitted from elsewhere. This gave a rate of 5.7/1000 live hospital births, and 165/1000 outborn admissions to the unit. The latter infants were predominantly of very low birthweight or were ill. Thirty-three of the isolates were cultured in the first 48 hours of life (early) and the remaining 80 after that time (later). Staphylococcus epidermidis was the organism most often isolated both early and later. These results were different from those recorded in the previous 9 years (1967--75) from the same unit. Then, group B beta-haemolytic streptococcus was the organism most often isolated early, while Gram-negative bacteria predominated among later isolates. The changing nature of care may contribute to these findings.