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AbstractValues of plasma amino acids (AA) in Taiwan Chinese in different age groups were determined. AA analysis was performed by ion-exchange chromatography. The results correlated well with the reference values published by Shapira in 1989, indicating that plasma AA concentrations are not evidently affected by race and dietary habits. We also confirmed the effect of age on plasma free AA levels. More than two thirds of 35 amino acids showed statistically significant differences between age groups (p<0.05, one-way ANOVA test). Levels of taurine, hydroxyproline, threonine, serine, glutamic acid, proline, citrulline and α-amino-η butyric acid varied with age (p<0.01). Only a few AA, including α-amino-adipic acid, glycine, alanine, cystine, homocystine, isoleucine, tyrosine, γ-aminobutyric acid and tryptophan, showed no statistically significant differences between the different age groups. When comparing the mean differences in individual AA among these three age groups using the post-hoctest, alanine, tyrosine, phenylalanine, glycine, glutamine, cystine, homocystine, isoleucine, γ-aminobutyric acid and tryptophan appeared to be constant across all age groups. Glutamic acid and serine correlated significantly with age (p<0.05), with a definite decline in concentration from infancy to adulthood (r=0.396 and 0.243; p<0.01, respectively). We conclude that AA values are not evidently affected by race, but they do vary with age.