Concentrations of tryptophan (free and protein bound) and its metabolites in plasma of maternal vein at delivery, umbilical vein, umbilical artery, neonatal vein and breast milk were determined by high performance liquid chromatography. The plasma levels of tryptophan and most of its metabolites in umbilical vein and artery were significantly higher than those in maternal vein. The concentration of total tryptophan in plasma of neonatal vein showed marked decrease at 24 h after birth in comparison with that at birth, but the total kynurenine concentration was not decreased in plasma of neonatal vein. The colostrum contained a high level of total tryptophan. There were high ratios of free to total tryptophan in colostrum, transitional and mature milk. In the blood, ratios of free to total of tryptophan and kynurenine were kept at constant level throughout the perinatal period.</p
