Over a two-year period 160 episodes of serious infection occurred in 139 infants admitted to a regional neonatal intensive-care unit. Eighty-seven (26%) of very low birth weight (VLBW) neonates and 52 (8%) of infants of birth weight greater than 1500 g were infected. The majority (84%) had bacteraemia alone. Though the clinical features of infection were not distinctive, in 94% of episodes the peripheral white blood cell or band counts were abnormal. Thirty-three (21%) of the infections occurred in infants under 48 h old and 15 of these followed prolonged rupture of membranes (greater than 48 h). All of the infections due to group B streptococci (5), Streptococcus viridans (2) and Haemophilus influenzae (3) occurred in this group. Coagulase-negative staphylococci (CONS) accounted for 49% of the infections and there was a marked increase in incidence of such infections during the survey. Infections with CONS were not necessarily associated with parenteral nutrition, the presence of intra-arterial catheters or mechanical ventilation but the rise in incidence was coincident with change in skin disinfectant usage and the general use of a third-generation cephalosporin to which the CONS were resistant. Although VLBW infants with meningitis were more likely to die than those of higher birthweight, the risk for those with bacteriaemia was the same in both groups. Infants with CONS sepsis were less likely to die than those with infections due to Gram-negative bacteria and the time from onset of infection to death was significantly longer for the former.