Lysophosphatidylcholine (LPC) has various stimulatory effects on many types of immune cells. The purpose of our study was to characterize blood LPC levels and to determine the composition of LPC molecular species (LPCs) in the neonatal period. Thirty-six neonates were enrolled in this study and then grouped according to birth-weight as follows: non-very low birth weight (NVLBW); >or=1,500 g (n=17), and very low birth weight (VLBW); <1,500 g (n=19). Sixteen healthy normal adults were used as controls. Levels of total blood LPC and LPCs (16:0-, 18:0-, 18:1-, 18:2-, and 20:4-LPC species) were measured using HPLC coupled with tandem mass spectrometry. Total blood LPC levels at birth in neonates in both groups (NVLBW and VLBW) were significantly lower than those of adult levels. In NVLBW infants, LPC levels reached adult levels at postnatal day 3 compared with VLBW infants, who attained adult levels after postnatal day 57 (around full-term). The composition of the LPCs was different not only between neonates and adults, but between NVLBW and VLBW infants. These findings may be associated with the difference of immunity among adults, NVLBW, and VLBW infants.