Elevated rates of transepidermal water loss (TEWL) in plaques of human psoriasis and in the skin of essential fatty acid (EFA)-deficient rats were compared.Cutaneous application of sunflower seed oil to EFA-deficient rats lowered the rate of TEWL to normal, healed the characteristic scaly skin of this condition and increased the incorporation of linoleic acid of the sunflower seed oil into epidermal phospholipid.Application of sunflower seed oil to psoriatic skin did not lower the TEWL, nor produce clin. improvement, but the linoleic acid of epidermal phospholipid was increased.Local application of a steroid ointment, clobetasol propionate (I) [25122-46-7] decreased the elevated TEWL in psoriasis and produced clin. improvement, but had no effect upon skin or plasma lipids.Application of this steroid to EFA-deficient rat skin cleared the skin scaliness but did not restore barrier function or change the composition of the skin lipids.Thus, the impaired barrier function in psoriasis is not due to EFA-deficiency.