Clinically significant staphylococcal septicaemia associated with the presence of bacteria in neutrophils in a routine peripheral blood film is described in four preterm infants. In all cases this allowed the diagnosis of infection prior to the result of microbiological cultures. It is likely that this finding is relatively common in this subgroup of patients resulting from a combination of severe infection associated with indwelling catheters and defective neutrophil bacteriacidal mechanisms. The findings in these cases suggest that careful blood film inspection in selected premature neonates may allow the early identification of sepsis.