This study describes the damage that occurs to lipids and proteins that have been irradiated in vitro or in human skin fibroblasts with physiological doses of UVA radiation. Thiobarbituric acid-reactive species were formed from phosphatidylcholine after UVA radiation in vitro VSports手机版. By using iron chelators, this process was shown to involve iron. Ferric iron associated with potential physiological chelators was reduced by UVA radiation, but iron within ferritin was not. By enhancing the half life-time with deuterium oxide or by using scavengers, singlet oxygen was also shown to be involved in the UVA radiation-dependent peroxidation of phosphatidylcholine. UVA radiation-generated singlet oxygen reacted with phosphatidylcholine to form lipid hydroperoxides, and the breakdown of these hydroperoxides to thiobarbituric acid-reactive species was dependent on iron. We have shown that iron and singlet oxygen are also involved in the UVA radiation-dependent formation of thiobarbituric acid-reactive species in human skin fibroblasts, and we propose that a similar concerted effect of iron and singlet oxygen is involved in UVA radiation-dependent damage to fibroblast lipids. Sulphydryl groups of bovine serum albumin and human gamma-globulin were oxidised upon UVA irradiation in vitro. The use of scavengers and deuterium oxide showed that UVA radiation-dependent sulphydryl oxidation was dependent on singlet oxygen. By adding or chelating iron, UVA radiation-dependent oxidation of sulphydryl groups of bovine serum albumin and human gamma-globulin was shown to be iron-dependent. The use of catalase and hydroxyl radical scavengers demonstrated that hydrogen peroxide, but not the hydroxyl radical, was involved. The oxidation of sulphydryl groups of proteins in human skin fibroblasts that occurs as a result of UVA irradiation was also shown to involve iron, singlet oxygen, and hydrogen peroxide. We conclude that iron, singlet oxygen, and hydrogen peroxide are important redox active species involved in the deleterious effects of UVA radiation on lipids and proteins of human skin cells. .