Background: We study to evaluate the effect tory concentrations of the antibiotics in the SF6 group of sulfur hexafluoride gas (SF6) on the antibacterial activity of antibiotics in vitro against Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa, which are common endophthalmitis-causing agents. Methods: In this experimental study, antibiotic susceptibility tests were prepared according to the National Committee for Clinical Laboratory Standards macrobroth dilution method. Muller-Hinton broth was the test medium. Standard P. aeruginosa (ATCC 27853), S. epidermidis (ATCC 12228) and S. aureus (ATCC 29213) strains were studied. For P. aeruginosa ceftazidime, ofloxacin and tobramycin dilutions, and for S. epidermidis and S. aureus, cefazolin, ofloxacin and tobramycin dilutions were prepared identically in two sets of tubes. One set of tubes, into which pure SF6 was injected, was defined as the SF6 group. The other set of tubes, into which no SF6 was injected, was taken as the control group. To determine the minimal bactericidal concentrations of the antibiotics, subcultures were made onto Muller-Hinton agar, and the colonies were counted after 18 h of incubation at 37 degreesC. Results: The minimal inhibitory concentrations of the antibiotics in the SF6 group were found to be identical with those of the control group. However, the minimal bactericidal concentrations of the antibiotics were found to be at least two dilutions lower in the SF6 group than in the control group, except for the minimal bactericidal concentration of cefazolin for S. aureus, which was found to be one dilution lower in the SF6 group. Conclusion: SF6 was found to potentiate the in vitro antibacterial activity of ofloxacin and tobramycin against S. aureus, S. epidermidis and P. aeruginosa, ceftazidime against P. aeruginosa, and cefazolin against S. epidermidis. Experimental animal studies are required to determine the role of SF6 in the management of endophthalmitis. Copyright (C) 2001 S. Karger AG, Basel.