Skin represents one of the extrapineal sites of melatonin (Mel) synthesis. In the skin Mel plays, for example, the role of an antioxidant which scavenges and inactivates free radicals arising due to UV irradiation. Although the protective effect of Mel on skin and cells irradiated mainly with UVB has been documented, to date no comparison has been made for the effects of Mel on cells exposed to UVA. Our study aimed at evaluating the effect of Mel (0, 10(-3), 10(-6) or 10(-9) M) added to culture medium 30 minutes before exposure of keratinocytes and fibroblasts to irradiation with UVA (15 J/cm(2)) and UVB (30 mJ/cm(2), 60 mJ/cm(2)). Viability of the cells was evaluated using sulphorhodamine (SRB) colorimetric test. Mel at 10(-3) M increased the number of surviving keratinocytes and at 10(-6) M increased the number of surviving fibroblasts exposed to UVB (30 mJ/cm(2), 60 mJ/cm(2)) as compared to cells exposed only to radiation. In addition, 10(-6) M protected keratinocytes exposed to the dose of 30 mJ/cm(2). Mel at 10(-3) M exerted a protective effect on both types of cells irradiated with UVA (15 J/cm(2)). As documented by our studies, Mel protects skin cells from the action of UVA and UVB. The protective effect of different Mel concentrations might result from variable expression of melatonin receptors.