The authors submitted a detailed characteristic of the properties of 5-fluorocytosine and its applicability in the treatment of mycoses. They emphasize the advantages of pharmacokinetic parameters of this systemic antimycotic preparation and the possibility to combine it with amphotericin B. Based on their own results of laboratory tests they give an account of the spectrum of sensitive and resistant mycotic agents. According to the authors 5-fluorocytosine is not sufficiently appreciated in Czechoslovakia and it deserves more attention.