Lumbar cerebrospinal fluid (CSF) was obtained from children during and following treatment for acute lymphoblastic leukemia (ALL). One hundred ninety-two CSF samples from 50 subjects, which were selected to minimize the effects of the disease and its treatment (i.e., to approach "normality" as closely as possible), were analyzed for the monoamine precursors tyrosine (Tyr) and tryptophan (Trp) and the metabolites homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA). Levels of HVA (p less than 0.0001), 5-HIAA (p less than 0.002), and Tyr (p less than 0.05) decreased with age from 3 to 17 years. Significant correlations were observed between the acid metabolites HVA and 5-HIAA (r = 0.79) and between the amino acid precursors Tyr and Trp (r = 0.71). Within individuals, levels of all four compounds were relatively stable over time, with total mean coefficient of variation ranging from 20% to 25%. No significant sex differences for CSF levels of HVA, 5-HIAA, Tyr, or Trp were found. Assessment of CSF monoamine precursors and metabolites in children treated for ALL may provide a method for understanding the chronic effect of CNS trauma on the ontogeny of monoamine systems.