CD14 is present in macrophage, monocyte, and granulocyte cell membranes. Its soluble fraction (soluble CD14-subtype), named presepsin (P-SEP) is present in blood in association with infections, due to phagocy- tosis of microorganisms. Increased serum concentration of P-SEP was reported in adult patients with se- vere bacterial sepsis, however, reports on pediatric patients have been limited. In order to clarify if P-SEP increases in pediatric patients with bacterial sepsis, we conducted a study of plasma P-SEP concentration in children with various febrile diseases. Eighty-eight subjects (49 males, 39 females, 18 days to 168 months after birth, mean 3.2 years old) who admitted to our hospital were enrolled. Among them, blood culture was performed for 56 children. As control, twelve afebrile, non-septic children who admitted for routine cardiac catheter examinations for con- genital heart anomaly were enrolled. Blood was withdrawn on admission. Plasma was obtained within 24 hours after blood withdrawal, stored at 4 Celsius degree until assays. P-SEP was assayed using PATHFAST(TM) chemiluminescent enzyme immunoassay system (LSI Medience Inc, Tokyo, Japan). Together with P-SEP assays, blood culture, white blood cell count, serum C-reactive protein (CRP) and procalcitonin (PCT) were assayed. Local ethic committee approved this study. P-SEP concentration ranged 195 to 866 (median 445) pg/mL in patients whose blood culture was positive on admission (n=7). On the other hand, patients with blood culture negative (n=49) remained low level, 82.1 to 770 (median 242) pg/mL(p=0.046). Control subjects (n=12) showed significantly low concentration of P-SEP (mean 160, SD 189, ranged 79.4 to 411 pg/mL) compared to those from blood culture positive children (mean 487, SD 478 pg/mL, p=0.010). Though number of samples was limited, P-SEP may possibly act as a new mark- er of febrile bacteremia even in children. More study is needed for reference intervals for children. [Original].