The effect of three commercially available corticosteroid preparations on ultraviolet (UV) erythema reaction was studied in healthy volunteers. Four series of circles were marked on the skin of their backs. One half of the circle of each series received 0.01 ml of 0.05% betamethasone valerate, 0.1% triamcinolone acetonide and 0.01% hydrocortisone 17-butyrate dissolved in isopropyl alcohol or ethanol and was covered with impermeable plastic. 24 h later, the sites were irradiated with UV light from a Kromayer lamp during 2, 4, 8,16 or 32 sec. The reactions were evaluated 24 h afterwards. The suppression effect of corticosteroids was expressed as the blanching score (0–3). In a second series of experiments, the reversed sequence was tested: irradiation with UV light was followed by the application of corticosteroids (betamethasone and hydrocortisone). In both series of experiments the blanching effect of the corticosteroids was found to decrease with increasing UV dose. Corticosteroids applied after irradiation were found to have stronger blanching effects. With UV doses of 1 minimum erythema dose (MED), mean blanching scores of 2.3–3.0 were registered, while with doses of 4 MED or more, only small effects were noticed. The three corticosteroid preparations showed comparable suppression effe