The objective of the study was to clarify some mechanisms behind the relaxing effects of chlorzoxazone. Motor effects induced by vibration of the masseter and digastricus muscles were studied in seven subjects. The response was measured by means of simultaneous recordings of EMG of masseter and digastricus as well as bite force. The measurements were performed before as well as after oral administration of 250, 500 and 1000 mg chlorzoxazone. Since no effect of the medication was seen, it was concluded that the muscle relaxing influences of chlorzoxazone are not effective on segmental levels. Large interindividual differences in responses to vibrations were observed.