This study tested the hypothesis that rapidly expanded random pattern skin flaps demonstrate enhanced resistance to bacterial invasion from intradermal injection of Staphylococcus aureus in a porcine model. Sites for a 6 X 12 cm expanded, a 6 X 9 cm sham-expanded, and a 6 X 6 cm acute random pattern skin flap were outlined, but not elevated, on the backs of 14 white pigs. A 450-cc tissue expander inserted beneath the panniculus carnosus at the site for expansion was sequentially filled to the limits of skin viability each day for 5 days. At the sham site a tissue expander was similarly inserted but left unexpanded; the acute flap site was left undisturbed. On day 8, flaps were elevated, immediately sutured in place, and 0.1 ml of saline solution containing 10(7) Staphylococcus aureus inoculated intradermally at four corresponding sites in each flap and at three sites in normal skin. In seven animals these sites were at the proximal base of the flaps; in seven others the sites were distal. The resulting areas of erythema and skin ulceration were measured on each of the next 3 days and the measurements compared. At corresponding proximal sites, the mean area of erythema and ulceration measured over the next 3 days in expanded flaps (31.2 mm2) and in sham-expanded flaps (33.8 mm2) was significantly less than in acute flaps and control skin (47.5 mm2, 43.4 mm2, p less than 0.05). Measurements in the rapidly expanded flaps were not significantly different than those in the sham-operated expanded flaps.(ABSTRACT TRUNCATED AT 250 WORDS)