Although the general concept that chronic irritation is a carcinogenic stimulus is no longer ac- cepted, in certain conditions chronic inflammation in humans may predispose to neoplasia. One of the best examples is the chronic draining sinus, usually resulting from chronic infections such as osteomyelitis. Such chronic infections are relatively rare today; however, in the past, when bone infections were rather common, epidermoid carcinomas occasionally arose in the skin near chronic draining sinuses. The histology of these lesions before the production of the neoplasm demonstrated a peculiar type of hyperplasia of the squamous epithelium known as pseudo- epitheliomatous hyperplasia (Sommerville, 1953). Other sites of chronic inflammation consid- ered to be associated with higher incidences of neoplasia are the lower lips of pipe smokers and nevi or moles in locations on the body subject to chronic irritation, such as the belt region or the back of the neck. As has already been suggested and will be more thoroughly elaborated in subsequent chapters, chronic inflammation and, to a lesser degree, trauma stimulate cellular proliferation, which may increase the potential for the development of neoplasia (Chapter 9). In Chapter 7, we consider how trauma may enhance the production of certain experimental can- cers of the skin. There is also significant evidence that metastatic spread of malignant neo- plasms can be facilitated by trauma. However, there is no unequivocal evidence that either chronic irritation or trauma is directly causative of neoplastic transformation in the living ani- mal (Monkman et al., 1974).