Immediately after a patient with myoclonus epilepsy smoked a nicotine-containing cigarette, tetraparesis and hyperreflexia with ankle clonus developed, but disappeared within several minutes. During paresis, the H-reflex size of the soleus muscle increased, EEG showed more slow waves than before smoking, and the cerebral perfusion increased around the motor cortex as shown by single photon emission CT. A similar effect occurred when the patient chewed nicotine gum, and smoking a cigarette with a high nicotine content induced severe positive and negative myoclonus after the development of tetraparesis. Administration of the C6-type nicotinic antagonist mecamylamine not only countered the smoking effect, but ameliorated the spontaneous positive and negative myoclonus. Mecamylamine may prove useful for the treatment of positive and negative myoclonus in myoclonus epilepsy.