Measurement of monoamine metabolites in cerebrospinal fluid (CSF) has been one of the few methods available to study monoamine transmitter function in the human central nervous system (CNS). It has steadily proved to be of much use in clinical research of neurological and psychiatric diseases, in which altered functions of central monoamine neurotransmitters have been identified. In this work 3-methoxy-4-hydroxyphenylethylglycol (MHPG), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were quantified in normal CSF and in patients with untreated Parkinson's disease (PD) and olivopontocerebellar atrophy (OPCA). Normal CSF was obtained from 162 patients at the time of spinal anesthesia for surgery. Reference values for monoamine metabolites were established for normal adult lumbar CSF. Up to the age of 70 years no relation of monoamine metabolite concentration with age or sex were encountered. In individuals above 70 years of age higher levels of MHPG, HVA, and 5-HIAA were present in women, while in men only higher levels of MHPG could be detected. A strong correlation between 5-HIAA and HVA concentrations were observed in all groups. PD patients exhibited normal CSF metabolite levels, but an altered 5-HIAA/HVA ratio, favoring 5-HIAA. Dominant and recessive OPCA differed essentially in HVA concentration-diminished in the first group and elevated in the last. Comparing the results obtained in PD and dominant OPCA, we suggest that the decrease of CSF HVA in the latter group might not reflect nigrostriatal degeneration as we previously thought. Possibly another factor influencing dopamine function in the CNS is involved.