There is growing evidence about the role of neuroendocrine hormones in the regulation of the immune system. In the present study we have examined effects on different stages of phagocytic function of peritoneal macrophages from BALB/c mice induced by beta-endorphin. Peritoneal macrophages were incubated (30 min at 37 degrees C) in vitro with 0.22, 0.5 or 2200 ng/ml of this hormone. Adherence capacity was evaluated by means of a substrate adherence technique, chemotaxis in Boyden chambers, and ingestion of Candida albicans on migration inhibitory factor (MIF) dishes. No changes in adherence capacity were found. Chemotaxis, however, increased, and concentration of beta-endorphin correlated directly with stimulation. Incubation of macrophages with 0.5 ng/ml of beta-endorphin also stimulated phagocytosis of Candida albicans. These results indicate that beta-endorphin acts on peritoneal marine macrophages, stimulating some stages of their phagocytic function.