This study was designed to examine the possibility that some occlusive dressings are barriers to wound penetration by pathogenic bacteria. Two common skin pathogens, the nonmotile, Staphylococcus aureus, and the motile, Pseudomonas aeruginosa, were used to challenge dressings placed on partial-thickness wounds in swine. S. aureus was recovered from 100% of air-exposed wounds (log, 5.5 ± 1.1) and from 50% of Op-Site-treated and Vigilon-treated wounds (log, 6.1 ± 1.1). S. aureus was not isolated from DuoDERM-covered wounds, P. aeruginosa was recovered from 100% of air-exposed wounds (log, 5.1 ± 0.5) and 100% of Op-Site-covered and Vigilon-covered wounds (log, 5.8 ± 1.8). P. aeruginosa was not recovered from DuoDERM-covered wounds. These studies lend support to the idea that dressings may protect wounds from invasion by pathogenic bacteria and demonstrate the need to evaluate their bacterial barrier properties in situ.