We have reported in our previous study that macrophages constitute 58% of the total number of white cells in noninfected neonatal cerebrospinal fluid (CSF). CSF macrophages are probably derived from blood monocytes. To explain their predominance, we compared the chemotactic response of monocytes from cord and adult blood to neonatal (NCSF) and non-neonatal spinal fluids (NNCSF). Zymosan-activated serum (ZAS) was used as a positive control. Significance was accepted as p less than or equal to 0.05. We observed that both random migratory (RM) activity and chemotactic responses (CM) of cord monocytes to neonatal CSF and ZAS were greater than those of monocytes obtained from adult blood, resulting in a significant increase in the chemotactic differential (CD). Chemotactic responses of neonatal monocytes were significantly greater in the presence of neonatal CSF as compared to CSF from older children as indicated by CD. The CD of neonatal monocytes to neonatal CSF was greater than that of neonatal neutrophils. These findings are consistent with the presence of specific monocyte chemotaxins in noninfected neonatal CSF.