The pharmacokinetics of [75Se-L]-selenomethionine was studied in 10 patients with psoriasis, 10 with atopic dermatitis and 10 healthy subjects. Values for the gut absorption and the rate of endogenous excretion of [75Se-L]-selenomethionine, the exchangeable total-body selenium and plasma selenium concentration showed no significant differences between either patient group and the controls. The results suggest that there is no gross abnormality of selenium pharmacokinetics in either disease, and fail to explain why previous studies have found reduced selenium concentrations and selenium-dependent glutathione peroxidase activity in psoriasis and atopic dermatitis.