Benzodiazepines (BDZ) are psychotropic drugs largely used in patients with affective disorders. As far as their effects on the immune system are concerned, a few studies have been carried out until now. Diazepam is inhibitory in vitro for the phagocytic functions and the antibody synthesis, being its action mediated via specific receptors on immunocompetent cells. On the contrary, alprazolam results to be enhancing for the antibacterial activity exerted by normal human peripheral blood T lymphocytes in vitro. Taken together, these data point out the different role which BDZ play on the immune response.