Twenty-seven rabbits were treated with bilateral tibial osteotomy and compression plates. One tibia in each animal received three to 15 microamperes constant direct current for 21 days. The breaking strengths of the stimulated tibiae were higher in 19 animals, as compared to controls (70.4% stimulation rate). The mean value of the additional maximum stress to break the stimulated tibiae was 0.73 kg. Fifteen other rabbits were similarly treated but with electrical stimulation being applied to only one tibia in each animal. There was an increase in endosteal and periosteal callus formation and greater vascularization on microangiography of the callus and the stimulated side. The fissure gap at the osteotomy site was smaller, and bone in the fissure was mature lamellar bone only on the stimulated side. The uptake of fluochromes was greater on the stimulated than control untreated side. Both tibiae in each of five rabbits were doubly fixed with compression plates. A simulated piezoelectric potential was applied to one tibia in each animal. There was a 20 per cent higher calcium and phosphate content of the stress protected cortex, as well as an increased uptake of fluorochormes, in the stimulated tibia as compared to that of the control tibia in three out of five of the animals.