The purpose of this investigation was to establish that epiphyses could survive and grow when preserving the endosteal and periosteal blood supply in free vascularized long bone including epiphysis grafts. These were compared to nonvascularized free bone transfers and normal controls. Sixteen mongrel puppies 4 months old, were used and were sacrificed 6 months later. Group I (Heterotopic radius transfers): On 8 puppies bilateral, heterotopic radius transfers were performed by exchanging the proximal 8 cm of the radius from one foreleg to the opposite one. In one foreleg the palmar interosseus artery and a concomitant vein were anastomosed to the recipient site vessels after bone fixation, while in the other one vessels were not anastomosed. Group II (Orthotopic radius transfers): On 8 animals in one foreleg, the proximal 8 cm of the radius was excised and replaced to the original site with vascular anastomoses. In opposite foreleg, radiopaque metal marker was inserted in the shaft Scm distal to the radial head for radiological investigation of growth which served as normal controls. All animals were followed with serial scanograms immediately, 2 weeks and 4 weeks postoperatively, and then monthly for 6 months after surgery. Brachial arteriograms were made 4 months after operation. Results: In Group I and II, X-ray showed solid bony unions at the osteotomy sites. In all 16 instances of vascularized bone grafts, the anastomosed vessels were patent on arteriograms performed 4 months postoperatively. The proximal radial epiphyses closed by 2 weeks to 1 month in nonvascularized heterotopic grafts. In vascularized heterotopic and orthotopic grafts, the proximal radial epiphyses closed at 5 months. In normal controls, the epiphyses closed at 6 months. In the vascularized heterotopic grafts, the longitudinal growth of grafted bones averaged 1.5 cm (12% increase to the initial entire radii). In the vascularized orthotopic grafts, the longitudinal growth averaged 1.6cm(13% increase). In the nonvascularized heterotopic grafts, the growth averaged 0.3cm(3% increase) and in the normal controls the growth averaged 2.4 cm (21 % increase). There were statistically significant differences in the final growth between the normal controls and the vascularized orthotopic grafts(p<0.025) or the vascularized heterotopic grafts(p<0.010), and between the nonvascularized grafts and the vascularized orthotopic grafts (p<0.005) or the vascularized heterotopic grafts (p<0.010). No significant differences were found between the vascularized orthotopic and heterotopic transfers (p>0.500). The growth in the vascularized grafts was 65% of normal radial growth.