The Scandinavian Mycosis Fungoides Study Group has treated 21 patients with mycosis fungoides in plaque stages with topical, whole-body application of nitrogen mustard, 20 mg in 40 ml water per square metre. Ten patients were treated after previous attempts at intravenous tolerance induction ad modum van Scott & Kalmanson and eleven without. Complete remission was initially achieved in 10 patients and partial remission in 9 patients. Contact dermatitis to nitrogen mustard developed in 2/10 after tolerance induction and in 1/11 without tolerance induction. It is concluded that topical, whole-body application of nitrogen mustard gives high remission rates. In this series, however, many relapses occurred, due to inadequacy of the maintenance treatment. Tolerance induction has not been found of any value.