Abstract
Ultrasonic therapists (9) and 9 controls were studied with regard to vibration perception thresholds within the frequency range of 5-400 Hz. Thresholds on the tip of the index and middle finger for both left and right hand were studied. In contrast to the controls, the therapists were exposed professionally to local vibration with high frequencies, around 1 MHz, from the handles of ultrasonic transducers used for therapy in medical service. For the therapists, compared with the controls, a reduction of vibration perception was seen. Vibration with high frequencies might have a negative influence on man.