Coagulase-negative staphylococci obtained from patients with continuous ambulatory peritoneal dialysis-related peritonitis were cultured in nutrient broth in an atmosphere of air containing 5% carbon dioxide (reflecting the CO2 tension found in freshly used dialysate). Significant differences were observed between the surface chemistries of cells grown in the two atmospheres, as determined by X-ray photoelectron spectroscopy and changes in the cell wall protein profile. The growth atmosphere also influenced the adherence potential toward polystyrene and silicone in a proportion of strains examined. Thus, gaseous conditions can profoundly influence the nature of the staphylococcal surface, and this should be considered in any in vitro study of in vivo behavior.