6 cases with acute febrile neutrophilic dermatosis (Sweet's syndrome) responded rapidly and dramatically to treatment with potassium iodide. All patients became afebrile and symptom-free within 24--48 h after therapy. The cutaneous eruptions subsided completely in 3--5 days. 5 of the patients received the drug only for 2 weeks, but they have had no recurrences. Although the remaining 1 patient had shown minor recurrences after cessation of the medication, he was free of all symptoms during the therapy. The mode of the action of potassium iodide is also discussed.