Polysporin First Aid Antibiotic Spray (Burroughs Wellcome Co., Research Triangle Park, N.C.) is a dry spray containing 200,000 units Aerosporin (polymyxin B sulfate) and 10,000 units bacitracin zinc, along with a propellant. Each 1-second spray delivers approximately 2300 units of polymyxin B sulfate and 115 units of bacitracin zinc. This study was designed to evaluate the efficacy of Polysporin Spray against various clinical isolates. Blood agar plates were inoculated with a pure culture of each isolate. Polysporin was then sprayed in an area approximately 30 mm in diameter. The area of inhibition was measured and recorded after 18 to 24 hours of incubation. A clear zone at least 20 mm in diameter with surrounding edges of growth indicated sensitivity. A zone less than 20 mm in diameter or growth over the whole plate indicated resistance. Three hundred fifty-three clinical isolates (202 gram positive and 151 gram negative) were tested. The results show that Polysporin inhibits the growth of all the gram-positive organisms, including methicillin-resistant strains of Staphylococcus. The gram-negative organisms were also sensitive to Polysporin Spray, with the exception of Serratia marcescens, Morganella morganii, and Proteus mirabilis. This study suggests that Polysporin First Aid Antibiotic Spray may be effective for wounds contaminated with gram-positive and some gram-negative organisms.