During a double-blind clinical trial of a histamine (H2) antagonist (ranitidine) in monitoring allergic rhinitis, the clinical response, total serum IgE levels, and Parietaria IgE antibody levels were measured. Ranitidine induces an improvement in scores of subjective and objective symptoms, a decrease in total serum IgE levels, and no significant variations in Parietaria IgE antibody levels. Since H2 antagonists seem to induce these improvements by acting on suppressor T cells bearing H2 receptor, as shown in our previous studies, it is hypothesized that the lymphocytic subset that regulates the total IgE synthesis is not the same as that governing specific IgE synthesis.