[en] In order to visualise the morphological changes of Epidermophyton floccosum associated with exposure to perdeuteriated n-hendecanoic acid, the architecture of the dermatophyte was investigated by means of interference contrast and scanning electron microscopy. The mortphology of mycelia grown on substrate containing perdeuteriated n-hendecnoic acid, or the unlabelled analogue, was compared. The perdeuteriated n-hendecanoic acid produced a characteristic undulant effect of the hyphae. The characteristic wave-lake appearance of the mycelia looked similar to the curling effect occurring after treatment of dermatophytes with griseofulvin, but was not so pronounced. Perdeuteriated n-hendecanoic acid, unlike the unlabelled analogue, also seems to cause a reduction of the number of chlamydospores perforations of the macroconidia. The changes in the morphological structure of Epidermophyton floccosum exposed to perdeuteriated n-hendecanoic acid have been investigated. Morphological examination of mycelia exposed to this substance by interference contrast microscopy demonstrated a picture of defect hyphae and macroconidia. By the aid of scanning electron microscopy an attempt was made to obtain a better visualization of these changes at ultrastructural level