Homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA), and 3-methoxy-4-hydroxyphenylethylene glycol (MHPG) were measured in lumbar cerebrospinal fluid from a group of patients ranging in age from 1 week to 45 years. Quantitation of these biogenic amine metabolites was achieved using a gas chromatographic/mass spectrometric technique. The subjects had various specific disorders of the nervous system, though patients with movement disorders and biochemical defects known to affect the neurotransmitter systems examined in this study were specifically avoided. The results indicated a strong inverse correlation in children between CSF HVA and 5-HIAA concentrations and age. The decline in these metabolites with age appeared to be exponential. No significant age effect was observed for MHPG. The results indicate the importance of comparing CSF metabolite levels in children with values in age-matched controls.