In squirrel monkeys (n = 13), 20 mg/kg/day of TIQ was injected subcutaneously for 43 to 104 days. Behavioral scores of motor disturbance were analysed; ranging from 20/45 to 30/45 (mean 27.8 +/- 4.18). Dopamine, total biopterine and tyrosine hydroxylase (TH) were decreased in the substantia nigra of TIQ treated monkeys compared to saline treated monkeys (n = 5). Levodopa was administered in 5 TIQ treated monkeys and remarkable recovery was recorded in these monkeys for more than 2.5 hours. In mice 50 mg/kg/day of TIQ was similarly administered for 70 days. TH staining was negative in about half of the cells of the substantia nigra, but cell bodies were preserved intact when checked by cresyl violet staining. Importance of use of aged animals was indicated in this kind of study.