The aim of this study was to determine plasma levels of granulocyte colonystimulating factor (G-CSF) and the relationship with leukocyte count, neutrophil count, results of cultures and sepsis scores in neonatal sepsis. forty-three newborns with gestational ages between seven hours and 37 days with sepsis were included in the study. The severity of sepsis was reevaluated using Tollner’s scoring system. We analyzed complete blood count, peripheral blood film and plasma G-CSF. Blood and cerebrospinal fluid cultures were obtained. Plasma G-CSF levels were determined with double sandwich enzyme immunoassay method at first and 20^th days. Endogenous G-CSF levels were increased in patients who had increased sepsis score as well as in patients with neutropenia and leukopenia and who were blood culture positive for gram negative microorganisms. G-CSF levels were also increased in acute phase of infection versus late phase, and in preterm infants who had poor prognosis versus term babies. There was an inverse and linear correlation between neutrophil count and G-CSF levels. This study has shown that bacterial toxins are an important stimulator of G-CSF production possibly by a feed-back mechanism, and premature infants are capable of producing sufficient levels of G-CSF. Anahtar Kelimeler : Yenidoğan sepsis, sitokinler, nötrofil sayısı,neonatal sepsis, cytokines, neutrophil count.