On March 5, 1957, a 10-year oId female terrier cross was admitted to Stange Memorial Clinic with a large firm tumorous mass (15 by 8 by 7 cm.) , which involved the proximal end of the radius and ulna. The leg was ankylosed in a flexed position with atrophy 'Of the muscles dorsal to the scapulo-humeral articulation. The animal suffered a fracture of the left front leg at about 1 year of age. An enlargement was noted in the area of the neoplasm about a year prior ta admittance ta the clinic, with a rapid increase in size of the area 1 month prior to entry.