A 48-year-old Japanese woman suffering from acute febrile neutrophilic dermatosis was hospitalized. The skin lesions included pea to thumb sized nodules and plaques that were edematous, flat elevated and oval shaped. Laboratory data disclosed high ESR, neutrophilic leucocytosis and positive CRP. Histological findings showed dense perivascular infiltration consisting mainly of neutrophils and nuclear dusts.An immunofluorescent study demonstrated deposits of IgM and C3 on the vessel walls, suggesting Arthus's reaction in the vessel walls as a cause of the subsequent pathologic changes in the.skin,