The objective of the present study was to explore the ability of eosinophils to present Strongyloides stercoralis antigen in naive and immunized mice. Antigen-pulsed eosinophils were injected intraperitoneally into naive or immunized mice, and then mice were examined for antigen-specific immune responses. A single inoculation of antigen-pulsed eosinophils was sufficient to prime naive mice and to boost immunized mice for antigen-specificT helper cell type 2 (Th2)immuneresponses with increased interleukin (IL)-4 and IL-5 production. Mice inoculated 3 times with live eosinophils pulsed with antigen showed significant increases in parasite antigen-specific immunoglobulin (Ig)Mand IgG levels in their serum. Antigen-pulsed eosinophils deficient in major histocompatibility complex class II molecules or antigen-pulsed dead eosinophils failed to induce immune responses, thereby demonstrating the requirement for direct interaction between eosinophils andTcells. These experiments demonstrate that eosinophils function as antigen-presenting cells for the induction of the primary and the expansion of the secondary Th2 immune responses to S. stercoralis in mice.