The purpose of the present study was to determine the immunologic responses, particularly immunopathologic reactions, associated with nasal immunization with the mucosal adjuvant, cholera toxin (CT). BALB/c mice were nasally immunized with tetanus toxoid (TT) combined with CT, and the responses of these mice were determined. After nasal immunization, mice produce a serum antibody response, primarily of the immunoglobulin G (IGG) isotype of predominantly IgG1 subclass, against both TT and CT. Along with the antibody responses, we also found that inflammatory reactions, which could be potentially fatal, developed within the lung. Furthermore, IgE responses were also induced after nasal immunization, and these responses were associated with the detection of interleukin 5 in the serum. Thus, nasal immunization with TT plus CT likely results in the activation of Th2 cells, which may contribute to serious immunopathologic reactions in the lung.