We have used a laboratory model of footshock stress in rats to determine whether stressor-induced alterations can be induced in polymorphonuclear leukocyte (PMN) function. We studied the ability of peripheral blood PMN to ingest and kill gram-positive bacteria. A single, 1-h session of footshock stress did not alter the ability of PMN to ingest or kill bacteria. However, 3 consecutive days of a 1-h session of footshock stress significantly enhanced the phagocytic activity of PMN but suppressed the ability of PMN to kill bacteria. Thus, this experimental model suggests that both the phagocytic and killing functions of PMN can be altered by repeated exposure to a stressor.