We prospectively evaluated the capacity of serum procalcitonin (PCT), compared with serum levels of C-reactive protein (CRP) and endotoxin, to identify children at high risk for mortality from sepsis after BMT. Of 47 pediatric bone marrow transplantation patients studied, 22 had an uneventful course post-transplant (Group 1), 17 survived at least one septic event (Group 2), and eight died from multiorgan failure (MOF) following septic shock (Group 3). Median concentrations of PCT over the course of the study were 1.3, 15.2, and 102.8 ng/ml, respectively, in each of the three groups (P<0.002 for each comparison). Median concentrations of CRP were 91, 213, and 260 mg/l, respectively (P<0.001 for Group 1 vs Group 2 and Group 3; P=NS for Group 2 vs Group 3). Median concentrations of endotoxin were 0.21, 0.30, and 0.93 U/l, respectively (P=NS for each comparison). Median concentrations of PCT, in contrast to serum CRP and endotoxin, correlated with the severity of sepsis (8.2 ng/ml in 'sepsis' and 22.3 ng/ml in 'severe sepsis', P=0.028) and provided useful prognostic information during septic episodes.