As a results of a depletion of atmospheric ozone all living organisms on the earth"s surface may be exposed to increased amounts of ultraviolet radiation. In man, ultraviolet radiation (UVR, especially UV-B) can cause, in addition to some beneficial effects like vitaming D formation, deleterious effects on the human health. Examples are diseasesof the skin, like erythema, photoageing and skin cancer and diseases of the eye, like keratitis and cataract. There are reasons to believe that UV-B radiation depresses the immunity against tumours and infectious diseases. It was demonstrated that UV-B suppresses the resistance against UV-induced tumours in mice and that this suppression is transferable to other mice if lymphocytes of UV-irradiated animals are used. Clinical research showed the induction of suppressor cells and inhibition of the NK activity by exposure to sunlight. UV-B can interact in diffrent ways with the immune system; antigen-presenting cells in the skin can be affected, the homing of lymphocytes may be distrurbed and the amount of suppressor cells often increased. More research is needed to establish relations between depressed immunity and decreased resistance against infections and tumours, so that these can serve as the basis for risk assessment of UV-B<br>