1. Oral immunization of mice with influenza virus type A/Udorn, induced antigen-specific IgA antibodies in external secretions (e.g., saliva and fecal extract). 2. Increased numbers of antigen-specific IgA spot-forming cells (SFC) were seen in mononuclear cells isolated from IgA-effector tissues (e.g., SG) of mice orally-immunized with influenza virus. 3. Following oral or systemic immunization of mice, IFN gamma-secreting cells (Th1 type) displayed a characteristic pattern of distribution which was related to the route of immunization.