Increasing evidence suggests the involvement of the basal ganglia in HIV-1-infected patients. We used SIV-macaques, an animal model of HIV-1 infection, to investigate changes in CSF biogenic amine metabolites over time and compared them with control animals. The dopamine and serotonin metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA), were analysed by reverse-phase chromatography with electrochemical detection. DOPAC concentrations were significantly increased in SIV-infected animals compared with controls. 5-HIAA and HVA remained unchanged. However, the longitudinal assessment of metabolites up to 3 months post-infection revealed a significant increase in 5-HIAA. Our results reflect the effects of SIV early stage infection on monoamine systems in brain and further validate the simian model for AIDS research.