The subpopulations of peripheral blood lymphocytes were identified using monoclonal antibodies specific for T lymphocytes (T11 antibodies), B lymphocytes (B1 antibodies), helper/inducer T cells (T4 antibodies) and suppressor/cytotoxic cells (T8 antibodies). Ninety-six subjects, including twenty-five patients with allergic asthma, nineteen patients with non-allergic asthma and fifty-two controls without asthma, were studied. There was no significant difference in the lymphocyte subsets between the allergic and non-allergic asthmatics. When comparing patients with asthma as a group with the controls, a decrease in the number of T8-positive suppressor cells and therefore, an increase in the helper/suppressor cell ratio were demonstrated in the asthamtics. A relative deficiency of suppressor T cells may represent another immunological marker of bronchial asthma.