The depletion in stratospheric ozone and changes in life-styles are likely to lead to an increased exposure to sunlight, including the UV-B waveband. Such irradiation may induce immunomodulation and therefore have adverse effects on human health. Alterations in immune responses could affect not only photocarcinogenesis but also resistance to infections, certain allergies and autoimmunity, and vaccination efficacy. In the present study, the risk of increased UV-B exposure has been estimated with respect to the resistance to a bacterial (Listeria monocytogenes) and a viral (herpes simplex virus) infection. The data indicate that suberythemal UV-B irradiation can have significant effects on immune responses to certain infectious diseases in human subjects.