Non-union of a fracture at the junction of the middle and lower thirds of the tibia was produced experimentally with associated trauma to the soft parts, resulting in swelling and compression of the vascular supply to the fragments. The results support the theory that occlusion or partial occlusion of the blood supply to the fracture site is an important factor in the production of non-union. The use of campiodol for visualization of the vascular tree offered an excellent method of control and substantiated the earlier results.