The regional distribution of pipecolic acid (PA) in newborn mouse brain, measured by a new sensitive high performance liquid chromatography with electrochemical detection (HPLC-EC) method, shows a two-fold difference among various areas. Diencephalon, olfactory bulb and anterior telencephalon show the highest PA levels, while the lowest PA levels are seen in mesencephalon and rhombencephalon. The pattern of regional distribution of PA is identical to the regional accumulation in brain of the newborn seen by us following i.p. injections of D,L-[3H]PA9. The highest levels of PA are seen in both brain and serum during the perinatal period of development. Pipecolic acid levels decrease in brain and serum at one day of age and reach adult values within two weeks postnatal. The brain/serum PA ratio (2.9-3.5) during the perinatal period declines gradually after birth to adult values (0.7-0.8) at 30 days. The liver and kidney follow the same pattern with higher levels of PA seen during the perinatal period; however, these levels decreased rapidly to adult levels within one week postnatal. Following injections (250 mg/kg, i.p. and s.c. in the adult and newborn, respectively), D,L-PA accumulates for up to 24 h in the newborn mouse brain. In adult, the cerebral concentration of PA increases rapidly and reaches its peak level in 5-10 min. It remains relatively constant up to 5 h and then declines slowly to 24 h. Pipecolic acid levels in serum show essentially the same pattern of accumulation between adult and newborn mice with some quantitative differences.(ABSTRACT TRUNCATED AT 250 WORDS)