Lung uptake of intravenously injected Tc-99m-HMPAO is observed in smokers and in lung toxicity due to various agents. We investigated the Tc-99m-HMPAO uptake of bronchoalveolar lavage (BAL) cells in the lungs after incubation in in vitro conditions (6 patients), intravenous injection (IV) (7 patients) and inhalation (INH) (6 patients) of Tc-99m-HMPAO in order to show whether BAL cells are also responsible for Tc-99m-HMPAO uptake in the lungs. Cell/supernatant (C/S) count ratio was 7.0 +/- 3.5, 29.3 +/- 40.8 and 8.4 +/- 4.5 for in vitro, IV and INH groups, respectively. C/Sin vitro showed a positive correlation with % alveolar macrophages (r = 0.943, p = 0.0048) and a negative correlation with % neutrophils (r = -0.945, p = 0.0045). Cells/whole BAL fluid ratio correlated with the amount of daily cigarette consumption in INH group (r = 0.95, p = 0.0037). Tc-99m-HMPAO showed adherence to mucus after inhalation. Tc-99m-HMPAO diffuses into alveolar spaces after injection and is present in BAL fluid and BAL cells both after injection and inhalation. Glutathione concentration and oxido-reductive state of the epithelial lining fluid and BAL cells may influence the lung uptake of Tc-99m-HMPAO.