In order to determine whether the dissection of helper/inducer (CD4+) and suppressor/cytotoxic (CD8+) lymphocyte subsets with Leu 8 reagent would reveal any differences between allergic asthma patients and non-atopic controls, we compared in both groups the 'true helper' T cell subset (Leu 8- CD4+), responsible for the major helper effect, and one of the suppressor T cell subpopulations (Leu 8- CD8+). Peripheral blood mononuclear cells from sixty-nine individuals, including nineteen extrinsic asthmatics, fifteen intrinsic asthmatics, seventeen patients with chronic obstructive lung disease and eighteen healthy controls, were comparatively analysed. Although total CD4+ cells and total CD8+ cells were similar for all groups, we found in the extrinsic asthma patients group a significant increase in the number of 'true helper' T cell sublineage (Leu 8- CD4+) and of suppressor cells expressing Leu 8- CD8+ phenotype. Such imbalances may be implicated in the pathogenesis of atopic asthma.