A novel method is described for the extraction of DNAs from fungi and yeasts. Anhydrous hydrogen fluoride (HF) selectively cleaves their cell walls under mild conditions (for 5 min at 0°C), enabling the effective extraction of DNAs from organisms with a cell wall. A possible mechanism for this method concerning the selective cleavage of O-glycosidic linkages in cell walls has been described previously [(1977) Anal. Biochem. 82, 289–309]. The extracted DNA is intact: in fact, the yeast DNA is directly applicable for restriction analysis and transformation of Escherichia coli.