Percutaneous absorption of hydrocortisone was measured by determining plasma cortisol during dexamethasone suppression in 26 patients with widespread atopic dermatitis. The first and second days of treatment with applications of 1% hydrocortisone cream twice daily were studied separately in two groups of six patients, Plasma cortisol levels rose after the first two applications, reaching a maximum in 24 h. The levels then began to fall, indicating possible restoration of the skin barrier, In two other groups of seven patients, the second application was made with a cream base alone, Two types of cream base were studied, one with 60% water and the other with 30% water, With the base containing 30% water, a brief increment was seen after 2 h. On the basis of this pharmacokinetic study, treatment of acute dermatitis could be intensified by applying hydrocortisone cream twice a day on the first day, but from the second day onward one application a day seems to be sufficient.