Presented paper informs about clinical course and treatment of bilateral toenail disease of a 57-year-old woman. Results of mycological tests, carried out recently, were not always identical - on the first one Alter¬naria alternata was proved in the infected tissue, the second examination was negative. During the final one the presence of septate non-pigmentate hyphae in the tissue were detected by direct microscopy and Tri¬chophyton rubrum and Alternaria alternata were growing mixed in the culture. Long duration of the disea¬se (more than 20 years) and its frequent relapses are apparently an expression of well established syner¬gism of the both pathogens. History of the patient indicates that the primary pathogen represented some of dermatophytes, while the non-dermatophyte mould Alternaria alternata invaded the infected tissue secon-darily. In the discussion basic literature data concerning the occurrence, clinical course and etiology of an onychomycosis are summarized.

        Key words: onychomycosis - toenails - Alternaria alternata - Trichophyton rubrum - diagnostics