Beta-2-adrenergic agonists are often employed in the treatment of acute bronchostenosis. Following our recent investigations into the influence of some drugs (cromolyn, ketotifen, theophylline) on the immune response, in this study we analyzed the in vitro effects of fenoterol (beta-2-adrenergic agonist) on the immune response. The mitogen-(PHA)-induced proliferation of peripheral mononuclear cells (PMNC), the PMNC proliferation induced by anti-T3 and anti-T11 monoclonal antibodies (MAbs), the PHA-induced lymphokine--interleukin 2 (IL-2) and interferon-gamma (IFN-gamma)--production were studied in ten healthy volunteers. Since the plasmatic peak of fenoterol following a single inhalation of 200 micrograms is about 20 ng/ml, in the experiments herein reported the drug was tested in the cultures at concentrations lower, equal and higher than the plasmatic peak: respectively, 2, 20 and 200 ng/ml. Furthermore, for a more detailed study of T-lymphocyte activities, we also evaluated the effect of fenoterol on T-cell clone proliferation. Our results, which reveal no effects of fenoterol on the studied immunological parameters, acquire relevance when related to our previous reports showing a depression of the immunological response exerted by theophylline and ketotifen.