The efficiency of some components of the host defense system has been evaluated in 32 atopic patients with rhinitis, asthma or asthma and rhinitis. No alterations in components of complement (C3 and C4), serum immunoglobulins (IgG, IgA, and IgM) and neutrophil functional parameters were found. As expected, serum IgE values were higher than in controls. A decreased percentage of total circulating T lymphocytes, an increased percentage of la 1-positive cells, but normal values of OKT4- and OKT8-positive T lymphocytes were demonstrated. However, a greater heterogeneity in the distribution of the suppressor-cytotoxic subset was shown in atopic patients.