1) In the unanesthetized chronic cat the monosynaptic reflex responses were recorded from the masseter nerve or from the masseter and temporal muscles, after giving shocks to the trigeminal mesencephalic tract.2) In the para-sleep phase the monosynaptic reflex response was smaller than in the preceding ortho-sleep phase. Transient facilitation and depression were also found during para-sleep. Threshold for the reflex elicitation increased slightly during para-sleep.3) In awake relaxed state the reflex response was not larger than that of ortho-sleep.