An extensive literature has accumulated on the use of various tissues, metals, and synthetic materials for reinforcing hernia repairs and for bridging tissue defects. There is a wide difference of opinion concerning the necessity and value of such prostheses in hernia repair. It would appear that, too often, the use of these substances is based more on the personal experience and philosophy of the practicing surgeon than on factual data. A comprehensive review of the literature reveals that most laboratory studies have been concerned with evaluation of tissue reaction to an implanted material and its tolerance in the presence of infection. Little attention has been paid to the effects of such added material upon wound healing and ultimate tensile strength. The extensive clinical literature has concerned itself mainly with the number of complications from implanted prostheses and the incidence of hernia recurrence. Critical evaluation of the worth of prostheses becomes