13 mongrel puppies underwent at the age of 3-5 months epiphyseal transplantations of the distal part of the ulna. Some of these transplantants were immediately revascularized by microsurgical anastomosis, others were left without anastomosis. Growth was followed by X-rays over a period of 6 months. Non-revascularized transplants showed minimal growth and were partially absorbed whereas revascularized transplants showed continuing growth, achieving 2/3 of normal growth of the control legs.