The behaviour of aged skin transplanted onto nude mice was investigated to determine whether the skin maintains its histological features. Split-thickness skin grafts obtained from the unexposed skin on the thighs of healthy aged and young volunteers were grafted onto nude mice. A significant difference between the mean thickness of young versus aged epidermis was noted before transplantation (P less than 0.001). The epidermis of aged and young skin showed an increase in thickness following engraftment with a mean increase in epidermal thickness of 18.8% in the young (P less than 0.01) and 142.5% in aged skin (P less than 0.001). The number of blood vessels in the aged skin was significantly lower than in the young skin, but a remarkable increase was found post-transplantation. These findings indicate that part of the typical histological changes of unexposed aged skin are reversible.