In this study, we evaluated the predictive values of procalcitonin (PCT), C-reactive protein (CRP), interleukin-6 (IL-6) and serum amyloid A (SAA) for determining the clinical course in febrile neutropenic patients. Daily plasma analyses during the fever course were performed in 101 episodes with fever and chemotherapy-induced neutropenia (neutrophil count <0.5 x 10(9)/L). Procalcitonin (PCT) and IL-6 values were significantly higher in febrile episodes in patients who developed complications. Procalcitonin with a cut-off value of < or =0.4 ng/mL or IL-6 < or =50 pg/mL 3 d after fever onset indicated daily high negative predictive values (NPVs) (91-100%) for episodes with complications. No marker could predict deterioration; however, daily low plasma concentrations of PCT or IL-6 during the first 8 d of fever were found to be a good predictor of no subsequent complications in neutropenic patients and therefore to be a helpful tool for limiting anti-microbial therapy.