Flow cytometry (FC) usefulness for pulmonary reactive cell changes examination in interstitial lung diseases was assessed. Bronchoalveolar lavage (BAL) lymphocyte direct (two-color and three-color) phenotyping was carried out in 63 patients with sarcoidosis (subdivided according to the disease radiological stage and smoking status), 23 patients with systemic sclerosis (SSc) and 12 individuals exposed to silica dusts. 33 healthy volunteers were used as controls. Routine BAL cytology and peripheral blood lymphocyte (PBL) typing was performed in all tested subjects. FC results quality control was performed according to BD Simultest IMK Plus criteria (for PBL) modified by the author. The conventional lymphocytic gate (PBL light scatter based) was excluded, as the source of error in L-BAL subset analysis. Two-color L-BAL phenotyping and alveolar lymphocyte CD45FITC/SSC gating was found to be usually sufficient. However, in poor-lymphocyte materials (e.g. in healthy smokers) three-color method, using anti-CD45 PECy5 monoclonal antibody for staining each patient sample, should be considered. No significant changes in lymphocyte subsets were found in FC as compared with alkaline phosphatase immunocytochemical method. The prevalence of CD3+ cells with only a few lymphocytes expressing NK (CD3-CD16 or 56+), T suppressor (CD8+ 11b+) or B cell phenotype--as compared with PBL, was found in BAL of all examined subjects. CD8+ cell subset was dominated by T cytotoxic cell phenotype (CD8+ CD11b-) in all tested groups. L-BAL T cells expressed sensitized memory cell phenotype--CD4+ (CD8+)CD45RO+ in sarcoidosis, SSc and controls (the staining not performed in silica exposed persons). Characteristic BAL cytological and immunological pattern (lymphocytic alveolitis, increased CD4/CD8, high CD3(CD4)+HLA-DR+ percentage) was observed in pulmonary sarcoidosis. SSc patients showed reduced BAL CD4/CD8 ratio, due to T cytotoxic cell predominance (the changes were more distinct in the group with clinical pulmonary changes). Early activation marker (CD25) was expressed on the elevated percentage of BAL T helper cells in SSc. High CD4+CD25+ cell percentage was the most characteristic sign of lymphocyte activation in individuals exposed to silica. Summing up, the reference values for L-BAL subsets were proposed. CD4/CD8 ratio alterations in interstitial lung disorders should be interpreted as the local imbalance between T helper memory cells and sensitized T cytotoxic lymphocytes. FC characterization of alveolar lymphocytes provides insight into the pathogenesis of pulmonary diseases.