The purpose of this study was to determine the effects of conventional and intraoperative tissue expansion on the biomechanical properties of skin. Two 200-cc silicone tissue expanders were inserted subcutaneously in each of six young pigs. One expander was inflated conventionally (4 weeks) and the other intraoperatively (three times within 1 hr). A skin specimen was excised from each expansion site and each contralateral control site and tested under tension to failure. The sites were closed and allowed to heal for 4 weeks at which time another biopsy specimen was taken from each site. Histological observations and biochemical analyses were conducted. Also, tangent modulus and ultimate stress were determined from the mechanical response of each specimen. Results indicated an initial decrease in stiffness and ultimate strength for conventionally expanded skin. The mechanism for this decrease could not be explained via our current biochemical and histological techniques. Mechanical properties for conventionally expanded skin, after healing, were not significantly different than controls. The mechanical properties for intraoperatively expanded skin were not significantly altered with respect to controls, either at initial expansion or after 4 weeks of healing. The tissue "generated" as a result of intraoperative expansion in the porcine model is likely tissue recruited from the surrounding skin.