The incorporation of syngeneic and allogeneic bone grafts pretreated by freezing or demineralisation was studied in 10 rats. Fresh, decalcified, or frozen cancellous bone of syngeneic or allogeneic origin was transplanted to intramuscular pouches. Revascularisation was evaluated with radioactive microspheres; formation of new bone was assessed by incorporation of strontium, and resorption was assessed by measuring the reduction of graft weight. Three weeks after grafting, fresh syngeneic and allogeneic bone differed significantly in all three variables. Frozen syngeneic bone was revascularised significantly better than frozen allogeneic bone, but there was no difference in formation of new bone or resorption. There were no significant differences between syngeneic and allogeneic decalcified bone in any of the variables studied. We conclude that differences in incorporation between syngeneic and allogeneic bone grafts are reduced by pretreatment with deep-freezing or demineralisation. Both forms of pretreatment affect the incorporation of the grafts.