The antibacterial effect of a new type I interferon inducer, an yeast RNA-tilorone molecular complex (MC), was studied using a model of staphylococcal infection. The MC taken in experimental doses being optimal interferon-inducing ones accelerates the Staphylococcus aureus elimination from mice organisms accompanied by increased functional ability (phagocytosis and bactericide activity) of peritoneal macrophages. The conclusion is that the MC antibacterial activity detected is mediated by its interferon-inducing properties.