The aim of the present experiment was to study how hypnotic susceptibility and hypnosis affect motoneuron excitability. In a first trial, human subjects were selected according to their hypnotic susceptibility. In a second trial, the Hoffmann (H) reflex amplitude of the soleus muscle was studied in 3 groups: (1) highly susceptible subjects during hypnosis with standardized suggestions of simple relaxation, anesthesia, analgesia and paralysis (group I), (2) highly susceptible subjects (group II), and (3) non-susceptible subjects (group III) during long-lasting control conditions. Surface Ag/AgCl electrodes were used to stimulate the posterior tibial nerve using a constant current stimulator and to record the soleus EMG. Analysis of variance was performed on the data. The linear correlation coefficient within groups was evaluated. The H reflex amplitude decreased significantly during the recording session in groups I and II and there was no change in group III. In group I the effect of different suggestions could not be distinguished from the effect of hypnotic relaxation. The decrements in H amplitude did not differ between groups I and II, suggesting that the effect was related to personality traits rather than hypnotic induction.