BACKGROUND:Previous reports on the behavior of procalcitonin blood levels in diverse clinical conditions suggest that it is part of the activation of cellular immunity and is another acute-phase reactant. OBJECTIVE:To compare procalcitonin with C-reactive protein, a well-known acute-phase reactant, in a series of acutely febrile pediatric patients and to review recent literature on procalcitonin. METHODS:Procalcitonin and CRP levels were evaluated in 38 blood samples of pediatric patients who were admitted to the Dana Children's Hospital for evaluation of unexplained fever or for sepsis work-up. RESULTS:The parallelism between procalcitonin and CRP was found to be highly significant (P < 0.01). CONCLUSION:The rise of procalcitonin blood levels in febrile pediatric patients suggests that it is part of the acute-phase reaction, parallel with the CRP reaction.