Immune memory cells for antibody production in the lung respond to antigen challenges, providing an important pulmonary defence. However, studies reported here suggested that long-term antibody production in the lung might also be important in pulmonary immune memory. After localized lung immunization and challenges, antibody production of specific IgG and IgA continued in the immunized lung lobes of dogs for months after the last antigen exposure. In addition, the evaluation of lung immunity in dogs immunized and challenged 3 years or 5 years previously (without additional antigen challenge) showed significantly higher levels of specific antibody in lavage fluid from the lung lobe exposed to antigen than in lavage fluids from control lung lobes. Cells from blood or from control lung lobes did not produce significant levels of specific antibody in vitro, whereas cells lavaged from the immunized lung lobes were producing specific antibody. Therefore, long-term antibody production by cells in lung lobes exposed to antigen probably contributed to antibody levels in serum and unexposed lung lobes. Traditionally, lymphoid tissues are believed to be responsible for long-term antibody production. However, antibody production in the lung for years without repeated antigen exposure suggested that other tissues might also be important in long-term antibody production. Maintenance of localized antibody production in the lung would be an important pulmonary defence against infectious agents, but might also play a key role in hypersensitivity lung diseases.