Waldron-Mease, E., 1979. Post anesthetic myositis in the horse associated with in vitro malignant hyperthermia susceptibility. Vet. Sci. Commun., 3:45-50.Four horses ~ith clinical and biochemical evidence of post-operative myositls following halothane anesthesia and characterized by well localized (lumbar) to generalized rigidity and pain are described. Response to Dantrolene Sodium therapy at 4 mg/kg per os was dependent upon rapidity of administration following onset. In vitro exposure of muscle to halothane and caffeine revealed increased sensitivity when compared to control horses.