Abstract: Pigmented cosmetic dermatitis composes amajor sort of undesirable reactions induced by cosmetics,but the melanogenic efect of cosmetics can scarcely be detected with patch tests inhuman.In the present study,10 cosmeticproduc tsmost frequently used by the patients with pigmented cosmetic dermatitis and 8 ingredients contained in the cosmetics were paintedonto separate are as of the dorsal flank of brow nish guinea pigs folowing the method reported by Imokawa et al,then skin specimens were removed,the parafin imbeded sections were stained with H.E.,Schmorl's reaction was used to show melanin,and Bacher,Praver and That cher's dopa-oxidase reaction to study the melanogenic effect of the cosmetics and the ingredients.

Key words: Melanogensis, Cosmetics, Guineapig, brownish