Abstract: Guinea pigs sensitized with DNCB were divided into 3 groups, and treated with UVR, PUPA, and grenz ray respectively on the shaved skin of one side of the back with usual therapeutic doses, 2-3 times weekly for three weeks.Then, the DNCB challenge test was made on the irradiated and unirradiated skin of the symmetric side.Then the biopsies of the skin were taken for the examination of Langerhans cells(LCs).The result showed that these three physical factors could suppress the contact allergic reaction of the irradiated skin, and at the same time the number of LCs decreased markedly. The result of the study further demonstrates that the pathogenesis of the contact allergy of the skin is closely related to LCs, and suggests that UVR, PUVA, and grenz ray can be used in the therapy of contact allergic dermatitis.