An experimental skin lesion induced in rabbits by the bite of infected adult Ixodes dammini showed dense dermal interstitial inflammatory cell infiltrates composed of mononuclear cells (histiocytes and lymphocytes) and granulocytes. The prevalence of phagocytic cells in this experimental lesion motivated a study on the interactions of macrophages and neutrophils with Lyme disease spirochetes. Interactions as measured by uptake of radiolabeled spirochetes and by indirect immunofluorescence were enhanced by opsonization of spirochetes with immune serum and not significantly decreased by heat inactivation of the same. Phagocytosis was inhibited by treatment of cells with Cytochalasin B. Adherence of opsonized spirochetes to neutrophils was decreased by blocking Fc receptors with heat-aggregated IgG, suggesting an important role for this receptor.