Chemokines, a superfamily of polypeptide mediators, are a key component of immune surveillance and are implicated in the initiation of the inflammatory cascade. This study investigated whether serum concentrations of the chemokines regulated upon activation, normal T-cell expressed and presumably secreted (RANTES) and interleukin-8 (IL-8) change in the perinatal period because of the transition from intra- to extrauterine life, and compared determined values in mothers (MS) (n = 30) with those in their fetuses (UC), neonates (day of life 1 [N1] and 4 [N4]), and controls (CS) (n = 20). RANTES serum concentrations were higher in MS than in UC ( p < 0.006), N1 ( p < 0.0001), N4 ( p < 0.0001), and CS ( p < 0.0001). IL-8 serum concentrations in MS and UC, respectively, were significantly lower than in N1 ( p < 0.0002 and p < 0.0007) and N4 ( p < 0.0001 and p < 0.0001). Thus, after birth, neonatal serum concentrations of RANTES decrease, possibly because of elimination of the placenta (probable production site), and neonatal serum concentrations of IL-8 increase, possibly triggered by environmental antigenic stimuli to which the neonate is exposed.