Monocyte functions of Storrs strain muscular dystrophic (MD) chickens and Storrs control strain were compared. After short-term in vitro culture of monocytes, cells taken from Storrs MD chickens had a significantly lower incidence of cells capable of phagocytizing sheep red blood cells than did cells cultured from the control strain. In contrast, no difference was found in the ability of MD vs. control strain blood mononuclear cells to undergo in vitro chemotaxis in response to a bacterial culture supernatant. The study also revealed a distinct peripheral blood leukocyte profile of young MD chickens: elevated percentages and absolute numbers of granulocytes. The total leukocyte count in MD chickens was not significantly different from that of normal chickens. These findings extend previous observations concerning altered reticuloendothelial system function in MD strain chickens.