Experiments were performed on isolated neutrophils tested in vitro to investigate the role of adrenocorticotrophic hormone (ACTH), cortisol and recombinant human interleukin-2 (rhIL-2) in modulating porcine polymorphonuclear (PMN) leukocyte function. Elevated levels of cortisol, similar to that observed during stressful experiences, caused a decrease in PMN chemokinesis (P < 0.02), chemotaxis (P < 0.001) and luminol-dependent chemiluminescence. ACTH at concentrations reflective of high stress conditions reduced PMN chemotaxis (P < 0.02) and chemokinesis (P < 0.01). In vitro rhIL-2 reversed (P < 0.05) the cortisol-induced and ACTH-induced suppression of PMN chemokinesis. These data indicate that specific neutrophil functions in pigs may be impaired by stress-related hormones of the pituitary-adrenal axis and that IL-2 may reverse some endocrine-induced suppression in chemokinesis.