The role of T lymphocytes in atopic disease is of considerable importance because animal studies indicate that cells of this lymphoid series may influence reaginic antibody response. T lymphocyte subpopulations were studied in a group of 76 children with allergic respiratory disease. There was no statistical difference between atopic children with asthma and those with allergic rhinitis as compared with an age-matched control population of 20 non-atopic children in terms of levels of active T lymphocytes or total T lymphocytes. The results of this study do not support the concept of a T cell immunodeficiency in children with allergic respiratory disease.