"Waltzing Matilda", a 5-year-old Standardbred x Thoroughbred bay mare was ridden in four endurance trial rides at the Equine Research Park during the summer months of May and June of 1977. Several gluteal muscle biopsy samples were obtained. She was noticed to stumble occasionally with her pelvic limbs. At the end of June when the trials had ended, "Tillie" was turned out into a paddock at the Equine Park and remained there through the summer of 1978. In the fall of 1977 "Tillie" was observed to have an atrophy of the left gluteal muscles. On July 22, 1978, "Tillie" was once again observed in her paddock stumbling with her pelvic limbs and was considered to be lame or ataxic. Atrophy of the left gluteal muscles was still apparent.