Changes in cerebrospinal fluid neurotransmitter metabolites in 25 children younger than 1 year of age were analyzed to assess maturation of the central nervous system and were compared to cerebrospinal fluid from older children and adults. Significant inverse correlations (P less than .05) with aging were observed for tryptophan, 5-hydroxytryptophan, 5-hydroxyindoleacetic acid, kynurenine, tyrosine, dopa, dopamine, dihydroxyphenylacetic acid, homovanillic acid, norepinephrine, and 3-methoxy-4-hydroxyphenylglycol concentrations. There were no significant differences observed with respect to age in the cerebrospinal fluid serotonin, 3-hydroxykynurenine, and 3-methoxytyramine concentrations. This study suggests that changes in the major cerebrospinal fluid neurotransmitters occur with increasing age during the neonatal period. Because these findings are preliminary, additional patients require study.