There has been described a new, easy method of isolation and staining of epidermis from leaves and cotyledon of healthy cucumber and infected one with the fungus Pseudoperonospora cubensis Berk and Curt and from tomato leaves infected with the fungus Oidiurn licopersicum Cook and Massee. The epidermis was taken of with the use of transparent Scotch from the leaves and stained with toluidyne blue. This method is helpful in distinguising the differences in a structure of epidermis of healthy and infected leaves and in estimating the following: stage of development of the fungus on epidermis, number and size of haustorium in epidermis cells, number of spores of a fungus on the certain surface of the host leaf. This method is valuable because it enables to protect the material for a long time, which is very important during testing a big number of plants.