Previous studies from our laboratories have shown that UV-B irradiation at the site of an intradermal infection of herpes simplex virus (HSV) resulted in a higher incidence of zosteriform lesions and suppressed cellular immune responses to HSV in mice. In order to determine whether the production of T-cell-derived cytokine (IFN-gamma, IL-2 and IL-4) by immune cells from irradiated mice is also suppressed, we examined the production of cytokines by lymph node cells and spleen cells taken from UV-B irradiated, HSV type 1 (HSV-1)-infected mice. UV-B irradiation (120 mJ/cm2) prior to HSV-1 infection was found to markedly suppress IFN-gamma production compared to that of the non-irradiated control. IL-4 production was enhanced compared to IL-2 in the UV-B irradiated mice. These results suggest that alteration(s) in the cytokine production profile may therefore be involved in the development of severe skin lesions caused by HSV infection in UV-B irradiated mice.