Eight new potentiators of antifungal amphotericin B (AmB) activity, phialotides A to H, were isolated from the fermentation broths of the rare fungus Pseudophialophora sp. BF-0158. The structures of phialotides were elucidated by spectroscopic analyses, including NMR and MS, and degradation studies. Phialotides were novel polyketide glycosides consisting of a 1,3-dimethylbut-1-ene (C6-unit) repeating substructure and one to three hexopyranoses. None of the phialotides exhibited antifungal activity, whereas all potentiated AmB activity against several fungi. Phialotide F was the most effective potentiator of AmB activity against Candida albicans, with a decrease in the MIC from 0.50 to 0.016 µg ml-1 being observed in combination with phialotide F at 1.0 µg ml-1.