The precise nature of the underlying disturbance responsible for TTP is unknown, but recent work suggests that abnormalities of sodium channels play an important role. There are only a few electrophysiologic studies reported during an attack of paralysis of TTP and the electrophysiologic studies during paralytic attack in our two patients showed the following results, different only in severity. 1.Nerve conduction studies were normal in all the tested sensory nerves. Motor nerves showed normal conduction velocities, but low amplitudes of CMAPs except for median nerve. 2.Needle EMG showed markedly decreased insertional activities, and lowamplitude, short-duration, and polyphasic MUAPS, The recruitment patterns on maximal efforts were markedly reduced. There were no spontaneous activities. 3.Repetitive nerve stimulation of ulnar nerve showed significant incremental responses on digiti quinti muscle, marked during the early phase of stimulation. The degree of incremental responses was proportional to the frequency of stimulation.