We conducted a prospective study in 215 children, 3 to 36 months of age, presenting with fever > or = 39 degrees C without obvious origin, in order to evaluate the diagnostic value of procalcitonin (PCT) in detection of occult bacteraemia. PCT associated with white blood cell count constitutes an efficient screening method with sensitivity 100%, specificity 61.9% and positive and negative likelihoods ratios of 2.62 and 0, respectively.