To study the effect of glucose concentration and dwell time of dialysis fluid on peritoneal antibacterial defence, an experimental infection with Staphylococcus aureus was induced in rats. For this purpose rats were inoculated intraperitoneally with Staphylococcus aureus at different intervals after the administration of various dialysis fluids. Twenty-four hours later the numbers of bacteria and cells in the peritoneal cavity were determined. The number of bacteria was correlated positively with the glucose concentration. Furthermore, an inverse correlation between dwell time and the number of bacteria was observed. Neither finding could be attributed to a glucose-dependent growth of the bacteria or disruption of the killing capacity of peritoneal cells in vitro. A glucose-dependent increase in the volume of the peritoneal fluid could partially explain the differences found in vivo. It is concluded that the glucose in dialysis fluid impairs antibacterial defence in the peritoneal cavity and that longer dwell times enhance this defence.