This study investigated the effect of time after burn injury on the kinetics of polymorphonuclear neutrophil (PMN) chemotaxis to Staphylococcus aureus. Rats with 30% body surface area back burns, and nonburned control rats, received several identical inocula of S aureus 3, 6, and 10 days after injury, and in vivo chemotaxis was measured by tissue myeloperoxidase at varying intervals. Animals six and ten days postburn had a delay, as well as a decrease, in maximal chemotactic response. This delay in response appears to be another mechanism by which PMN chemotaxis is affected by burn injury.