Following topical immunization of the respiratory mucosa in man, persistence of antibody in the respiratory secretions can be demonstrated in some individuals for more than one year. The secretory response to replicating agents is generally more prolonged than the response to less persistent antigens. Repeat topical antigenic stimulation provokes a response which differs very little from the primary response in magnitude, duration or latency. Nevertheless, if more than 1 year following adequate primary intranasal immunization, at a time when secretory antibodies are no longer detectable, men are again vaccinated intranasally with a dose of formalin-inactivated rhinovirus vaccine which will not provoke a primary secretory immune response, some vaccinees will produce nasal antibody. Similarly in mice, a second topical immunization of the respiratory tract with a dose of tetanus toxoid which does not produce a detectable primary secretory immune response will cause 11S IgA antibodies to appear in bronchial and nasal washings. Thus, it is possible that the secretory immune system may possess certain attributes of immunologic memory as classifically defined by the responses of the internal immune system to repeated antigenic stimulation.