Nosocomial bloodstream infections (BSI) in premature neonates are an important cause of morbidity and mortality. The early and efficient diagnosis of a neonatal BSI and the differentiation between bacterial and fungal BSI remains a challenging task. We compared the clinical features and blood test results in preterm infants with proven candidal or bacterial BSI in order to identify potential risk factors for developing a candidal BSI. Preterm infants with proven candidal BSI were significantly more prematurely born (mean age of gestation 27.7 vs. 29.8 weeks), had previously received significantly more antibiotics of multiple classes (mean 4.4 vs. 1.2) for significantly longer periods (mean 19.3 vs. 3.2 days), were ventilated more intensively, had a significantly longer stay at the neonatal intensive care unit before the onset of the BSI (mean 26.5 vs. 9.4 days), and had C-reactive protein values even higher than in preterm infants with a bacterial BSI (mean 90 vs. 71 mg l(-1)). The presence of thrombocytopenia ( < 150 x 10(9) cells l(-1)) in all the preterm infants with candidal BSI was a significant difference. No differences were seen with regard to birth-weight, use of central intravascular catheters, total parenteral nutrition, white blood cell count and differentiation. In conclusion, candidal BSI can be strongly expected after the third week of admittance in the most premature neonates on a respirator and treated with multiple classes of antibiotics for a prolonged period of time. The presence of these risk factors in a 'septic' premature infant on antibiotic treatment justifies the empiric use of antifungals.