Malignant hyperthermia is defined as a potentially fatal hypermetabolic syndrome char-acteriged by hyperpyrexia, muscle rigidity, tachycardia, respiratory and metabolic acidosis. cyanosis etc. It ia susceptible in patients with musculoskeletal diaease such as strabismus, kyphosco-liosia, hernia, cleft palate, cryptorchidism, but there is no single diagnostic method to detect a susceptible patient. Fortunately s-CPK is elevated in 70% of carriers, so we checked a-CPK and a-LDH bel- ore operation in patients scheduled for correction of congenital strabismus and classified into group 1 (norirlal a-CPK group) and group 2 (elevated s-CPK group) . We administered Oantrolene sodium to group 2 before operation and compared the changes of s-CPK and s-LDH after operation. The results are as fallows, 1) s-CPK was lowered after administration of Dantrolene sodium in group 2 . (from 76.4 IU/L to 48.5IU/L) 2) s-CPK elevation after operation was much less in group 2 than group 1. (56.1±58.7 IU/L vs 164.7±127.1 IU/L) In conclusion, it would seem that Dantrelene aodium was affective in prevention of mali-gnant hyperthermia.