A corticocancellous core was removed from the lateral condyle of both femurs in 26 skeletally mature dogs. The cavity was treated with cryosurgery, phenol cautery or packing with bone cement. The animals were killed after 1, 4, and 12 weeks in the phenol and cement groups, and also after 24 weeks in the cryosurgery group. The extent of the bone necrosis and healing was assessed in each group. After cryosurgery the extent of necrosis was profound in that the area of damage was 365% compared to the area of the cavity; the depth of necrosis extended between 2.5 and 14 mm, beyond the cavity wall. The effect of phenol was negligible in that only microscopic areas of superficial focal necrosis were found around the cavity wall. Bone cement produced an area of necrosis of 153% compared with the cavity, with a depth of between 1.3 and 2.8 mm. Regeneration in the region of necrosis after cryosurgery was only scanty by 4 weeks, but by 12 weeks considerable areas of regeneration were identified and complete healing was observed by 24 weeks. Regeneration of the necrotized bone produced by bone cement packing was rapid and similar to that of the control specimens. These findings suggest that cryosurgery could play a significant role as a surgical adjunct to curettage in locally aggressive benign bone tumours and in some malignancies. Phenol cautery is not regarded as an adequate treatment after curettage of bone tumours. Although the extent of necrosis was relatively small, packing with bone cement is thought to be a useful choice in benign cases.