On Oct. 5, 1943, a 9-year-old, brown, riding horse was brought to the veterinary clinic with history and symptoms of stringhalt. When the patient moved at any natural gait, the left hind leg was flexed so that the hoof closely approximated the body. This condition may be defined as an involuntary flexing, affecting one or both posterior limbs. The limb is lifted with excessive suddenness and beyond normal flexion. Numerous investigators in their study of this myoclonic condition have advanced various theories in regard to the possible etiology.