Residual cholesteatoma was experimentally produced in guinea pigs by transplanting a free skin graft into the middle ear bulla. In group A, the graft was placed on the mucosa after scratching the surface with a pick, while in group B, it was placed on the bone surface following removal of the mucosa and drilling with a diamond burr. The group A procedure was conducted on the left ear and the group B procedure on the right ear in 12 guinea pigs. The animals were sacrificed at two, four and eight weeks after transplantation. In all 12 ears of group A, the graft kept its original flat shape, resembling an open type residue. In eight of 12 ears of group B, the graft grew forming a squamous pearl, while in the remaining four ears it retained a flat shape. The difference in configuration is thought to be due to the amount of granulation around the graft.