HYPERKALEMIC periodic paralysis (HPP) or adynamia episodica hereditaria is a familial disorder inherited as an autosomal dominant, with the onset in early life of episodes of flaccid muscle weakness during which there is a rise of the serum potassium (K+).1The paralytic episodes may be precipitated by the ingestion of potassium salts or by a period of rest following exercise. Many families with HPP also exhibit a cold-sensitive myotonia such as to suggest to some observers that adynamia episodica hereditaria and paramyotonia congenita of von Eulenberg are identical.2In any case, the diagnostic term, HPP, accurately defines the syndrome under discussion. It has been suggested on the basis of clinical and electromyographic findings that the paralytic attacks in HPP may be due to a reversible depolarization of the muscle fiber membrane.3-6Creutzfeldt et al were able to demonstrate a fall of the resting potential of muscle fibers