Cataplexy, an abrupt and reversible paralysis, has been observed in 50 rapid eye movement (REM) sleep narcoleptics. The attacks lasted from a very few seconds to as long as 30 minutes. During attacks, the electroencephalogram remained similar to the normal base line awake EEG recorded previously in each patient; however, there were short periods where REM sleep could not be eliminated. Electromyographic tracings recorded an abrupt drop of muscle tone during attacks, but the numbers of muscles involved varied from one attack to another. Normal jerk reflexes could not be elicited, and H-reflex, systematically studied in five patients, was abolished. An exceptional patient with "status cataplecticus" with more than 30 daily cataplectic attacks was given levodopa, L-hydroxytryptophan, and atropine sulfate intravenously in separate trials with no beneficial effect. Intravenously administered clomipramine hydrochloride suppressed the attacks dramatically.