Forty inbred hooded rats sustained a fracture of the left tibia and 2 animals had an additional fracture of the right tibia (44 fractures in 42 rats). Before the fracture, medullary nailing was done with a 0.8-mm stainless-steel wire. Forty-one of the 42 fractures were transverse, 7 of the 42 nails bent more than 15 degrees. Radiological union occurred within 3--4 weeks.