Units were recorded extracellularly in the cat brainstem under the effect of tremogenic doses of harmaline. They were localized post mortem and the units discharging at the harmaline tremor frequency were mapped. Harmaline-sensitive neurons were found in the bulbo-pontine reticular formation, in particular, in the lateral reticular nucleus and the nucleus reticularis tegmenti pontis. The nucleus interpositus as well as the red nucleus also displayed numerous units discharging at the tremor frequency, indicating that the cerebello-interposito-rubro-spinal system controlling the flexor muscles participate in harmaline tremor. Participation of the oculomotor system in the harmaline-induced tremor was tested at the level of the vestibular neurons relaying the vestibulo-ocular reflex, the motoneurons, the eye muscles and the eye movements. No rhythmic discharge at the tremor frequency nor eye movements could be detected, indicating that harmalie tremor does not affect the oculomotor system.