1-Benzyl-1,2,3,4-tetrahydroisoquinoline (1BnTIQ) was detected as a novel endogenous amine in mouse brain and parkinsonian CSF by using the gas chromatography-selected ion-monitoring method. The level of 1BnTIQ was very high in CSF of some parkinsonian patients compared with that of controls with other neurological diseases, the mean value being three times higher (parkinsonians: 1.17 +/- 0.35 ng/ml of CSF, n = 18; vs. controls: 0.40 +/- 0.10 ng/ml of CSF, n = 11; mean +/- SEM, not significantly different). The pole test, a toxicological examination to evaluate behavior abnormalities related to Parkinson's disease, was used to examine the pharmacological effect of 1BnTIQ in mice. Repeated administration of 1BnTIQ induced behavior abnormalities, which pretreatment with 1-methyl-1,2,3,4-tetrahydroisoquinoline could prevent. We suggest that 1BnTIQ may be related to the idiopathic Parkinson's disease.