We reasoned that persistent exposure to a limited set of airborne antigens could drive the preferential expansion of single T-cell clones in the lower respiratory tract of normal individuals. To explore this issue, the normal human alpha/beta T-cell receptor repertoire was studied in lung lymphocytes obtained by bronchoalveolar lavage (BAL) from the humen of the lower respiratory tract. BAL T-cells obtained from five healthy volunteers were first analysed using polymerase chain reaction to amplify all known V alpha and V beta genes of the T-cell receptor. T-cells from peripheral blood were used as an internal control. Heteroduplex analysis of the amplified products was then performed, to assess the clonal composition of the repertoire of lung- versus blood-derived T-lymphocytes within each amplified variable gene family. In all subjects, the T-cell repertoire in the lung was largely as heterogeneous as peripheral blood in terms of clonal composition. This indicated lack of preferential expansion of single T-cell clones. A few T-cell clones were simultaneously expanded in blood and lung in all individuals within a limited number of V beta (mean 2.4; range 2-4) and V alpha (mean 1.6; range 1-3) genes. We also found that lung T-lymphocytes expressed all of the V gene families of the T-cell receptor that were expressed by peripheral blood T-cells. Our results indicate that T-cell clones in the lower respiratory tract of normal individuals are distributed according to a largely polyclonal pattern, which corresponds to that found in peripheral blood.