The rate of delivery of homovanillic acid (HVA), a metabolite of dopamine, from brain to cerebrospinal fluid (CSF) was estimated as a marker of brain dopaminergic production in healthy young and old volunteers. HVA concentrations were measured in serial aliquots of lumbar CSF from 7 young and 7 older subjects, and CSF flow rate also was measured. A model was used, based on Fick's principle, to calculate the brain HVA production. Although HVA concentrations did not differ between the two age groups, HVA delivery from brain in the elderly group was 50% less than in the younger group, consistent with other evidence of reduced dopaminergic neurotransmission with age. Our method can be used to estimate delivery rates of other brain-derived substances found in CSF.