Receptors for the Fc portion of IgA (RFc alpha) were identified on human monocytes and polymorphonuclear cells (PMNs) by cytofluorograph analysis using FITC-labeled IgA and by rosette formation with IgA-sensitized indicator cells. Larger percentages of PMNs obtained from the oral cavity expressed RFc alpha than did blood PMNs. These oral PMNs also expressed more RFc alpha per cell than blood PMNs. Moreover, the expression of these receptors on blood PMNs was enhanced by overnight incubation with IgA. In functional studies, RFc alpha appeared to cooperate with receptors for IgG in enhancing blood and oral PMN mediated phagocytosis of target cells coated with IgG and IgA. Furthermore, and in contrast with blood PMNs, oral PMNs were capable of phagocytosing target cells coated with IgA alone. Thus, receptors for IgA may be important to the ability of RFc alpha bearing effector cell populations to mediate protection at mucosal surfaces.