The rectum as an effective site for induction of systemic and local immunity has received little attention. Rectal immunization with microspheres-containing ovalbumin (MS-OVA) was tested for its ability to elicit systemic and mucosal immune responses. Rectal immunization with MS-OVA enhanced both Th2 dominant OVA-specific IgG levels in the serum and OVA-specific IgA levels in fecal extracts more prominently than did oral immunization. Cytokine analysis of CD4(+) T cells indicated a predominant induction of Th2-type responses compared to Th1-type responses following rectal immunization compared to oral immunization. These results demonstrate that rectal immunization with microspheres could be an effective new vaccination method.