In 1963, Klein et al. first described two girls with normokalemic periodic paralysis and cardiac arrhythmia. We have observed a 15-year-old girl with cardiac arrhythmia and normokalemia but with some features of hyperkalemic, periodic paralysis. The patient showed a waddling gait and Gower's sign. She had atrophy of the proximal muscles and deep tendon reflexes were reduced. Her ECG showed bigeminy with multifocal premature ventricular contractions. At the start of an episode of muscle weakness, the serum potassium concentration rose from 3.1 to 4.4 mEq/l. Muscle weakness was not provoked by intravenous administration of 45 g glucose or of 72 g glucose followed by 10 units of regular insulin. Muscle weakness was evoked by the ingestion of 4 g potassium chloride. During the provoked muscle weakness, the ECG showed normal sinus rhythm temporarily.