ABSTRACTThe distribution of immune deposits in the skin of reversed passive Arthus reaction was investigated using horseradish peroxidase (HRP) as antigen. Free and non‐reacted HRP, after leaking from small vessels, spreads widely in connective tissue, in epidermis, and in hair follicles in a diffuse and homogeneous pattern. When a specific antibody is administered, HRP appears as granular deposits, which can be considered to be immune deposits, and they adhere to the tissues. When sufficient amounts of antibody is intracutaneously administered, these granular deposits are seen at the wall of venules or in the vicinity of the venules, but when a small amount of antibody is injected, the deposits are seen widely in the connective tissue and are apt to be accumulated at the basement membrane of the dermo‐epidermal junction and of hair follicles. Free HRP passes the basement membrane easily, but the immune complexes are considered unable to pass it and are deposited under