Previous studies have shown that beta-glucans extracted from yeast or fungi potentiate immune responses. In the present study, the immunomodulatory activities of beta-(1-->3,1-->4)-glucan, derived from oats, were investigated. The ability of oat beta-glucan (ObetaG) to stimulate IL-1 and TNF-alpha release from murine peritoneal macrophages and the murine macrophage cell line P338D1, was assessed. In vitro stimulation of macrophages with ObetaG resulted in the production of IL-1 in a dose and time-dependent manner, whereas only small amounts of TNF-alpha could be detected in the culture supernatants. ObetaG also induced the production of IL-2, IFN-gamma and IL-4 secretion in a dose-dependent manner in cultured spleen cells. The intraperitoneal administration of ObetaG in mice resulted in the accumulation of leucocytes, predominantly macrophages, in the peritoneal cavity. Furthermore, ObetaG was tested for its ability to enhance non-specific resistance to a bacterial challenge in mice. Survival of mice challenged with Staphylococcus aureus was enhanced by a single intraperitoneal administration of 500 microg of ObetaG 3 days prior to bacterial challenge. In conclusion, these studies demonstrated that ObetaG possesses immunomodulatory activities capable of stimulating immune functions both in vitro and in vivo.