Immunologic evaluation of vaccines has depended largely on the measurement of an antibody response in the serum of recipient animals. This approach, which worked well for diseases prevented in large part by humoral immunity, ignored the contributions cell-mediated immunity (CMI) or mucosal immunity make to providing protection against many infectious diseases. As a result of this approach, certain vaccines were marketed that produced a satisfactory antibody response but failed to protect vaccinates in the field from disease. In the modem biologics industry, there is increasing pressure for vaccine improvements and new technologic advancements to be based on a sound understanding of the entire basis for immunity, including cell-mediated, mucosal, and humoral immunity that develops after exposure to infectious disease agents.