AbstractChemotactic responsiveness to fMet-Leu-Phe in concentrations of 10−8to 10−4M in the Boyden chamber was compared between peritoneal exudate cells (PEC) and polymorphonuclear leukocytes (PMN) isolated from peripheral blood, between MRL/Mp-+/+ (MRL-+/+) and MRL/Mp-1pr/1pr (MRL-1pr/1pr) mice, and between young (6 - 9 week old) and aged (16 - 24 week old) mice. Chemotactic responsiveness of PEC did not differ between MRL-+/+ and MRL-1pr/1pr, and young and aged mice. While, PMN showed greater chemotaxis in aged MRL-+/+ mice than that in aged MRL-1pr/1pr mice. These results suggest that chemotactic responsiveness of PMN differ from that of PEC which is assumed to be preactivated by an inflammatory agent injected into the peritoneal cavity to elicit cells. Less responsiveness of PMN to the bacterial origin peptide might relate to the autoimmune disease of this murine model.