Behavioral changes and eye movements were studied through chronic low-
dose MPTP exposure (ten intramuscular injections of 0.2 mg/kg per day)
in four monkeys (Macaca rhesus). The monkeys developed the deficit of
spontaneous saccades and decreased oculomotor range. The vertical com
ponent of saccades were hardly reduced. The examination of vestibulooc
ular reflex revealed no changes (r = approximately 1.0), but the fast
phase of nystagmus was blocked.