Penetration studies of radiolabelled Triamcinolone acetonide from ointment or cream preparations revealed that in cases of normal as well as psoriatic skin 70-90% of the applied substance remains on the surface. Normal horny layer stores up to 30% of the steroid. Nevertheless, a rapid penetration into the living layers of the skin is observed, whereby the epidermal concentrations reach levels between 5-10(-6) and 3-10(-5) M (mol per liter of tissue). The excretion in the urine took more than 72 h after removal of the excess of substance from the skin. In psoriatic skin, the epidermal and dermal concentrations were 3-10 times higher than in normal skin. This increase lies in the same range as the one resulting from removal of the horny layer by stripping prior to the application, as reported earlier.