By the method of Jesenská and Danilla [29] the growth inhibition of vegetative hyphae of colonies of 12 species of dermatophytes and keratinophilic fungi on the surface of glucose-peptone-agar with incorporated griseofulvin has been established. It could be concluded that the sensitivity of hyphae to griseofulvin is neither connected with the taxonomic position and ecological classification of these microscopic fungi, nor with their ability to survive in the soil, or with their pathogenity etc. - In Trichophyton rubrum some hyphae were found which were extremely resistant to griseofulvin. - The extablished values allow to make an objective comparison of the sensitivity level of vegetative hyphae of dermatophytes and keratinophilic fungi to griseofulvin in further geographical regions, at different times and in different laboratories. - In the discussion further possibilities in this direction are developed.