Lymphocytes play an important immunoregulatory role in pulmonary immune responses. By releasing cytokines they can control the cell–cell communication of other participating cells. Although it is well established that the lung lymphocytes, localized in distinct compartments, differ in their subset composition, little is known about cytokine production in these compartments during immune responses. Lewis rats were immunized by intravenous administration of sheep erythrocytes on day 0 and day 7 and challenged intratracheally with sheep erythrocytes on day 10. Four days after intratracheal (i.t.) challenge the composition of lymphocyte subsets (CD2⁺, CD4⁺, CD8⁺, B cells, natural killer (NK) cells) in the spleen, blood, lung perfusate, lung tissue and bronchoalveolar lavage fluid (BALF) was characterized, and intracellular IFN-γ was detected in these subsets by flow cytometry. Comparing control and immunized animals, no changes were found in lymphocyte numbers, subsets or the percentage of IFN-γ-producing lymphocytes in the spleen, blood and lung perfusate. In lung tissue and BALF, however, the absolute number of all lymphocyte subsets and the percentage of IFN-γ-producing lymphocytes were increased. When the lymphocyte subsets were analysed an increased percentage of IFN-γ-producing T cells was found in lung tissue (4.5 ± 0.6% versus 12.8 ± 1.1%) and in BALF (7.8 ± 1.4% versus 14.8 ± 1.9%) of immunized animals opposed to controls, this increase being seen in both CD4⁺ and CD8⁺ cells. Thus, there is an accumulation of T cells with an increased potential to produce IFN-γ in the lung interstitium and the bronchoalveolar space during pulmonary immune responses.