Results of 3-year investigations of the occurrence of fungi of the order <i>Erysiphales</i> and their hyperparasite, <i>Ampelomyces quisqualis</i> in the Drawsko Landscape Park (N-Poland) are presented. Among the fungi found, 26 species belonging to 7 genera were identified. Many of the causal agents of the powdery mildews revealed were previously rarely found in Poland. <i>Microsphaera vanbruntiana</i> var. <i>sambuci-racemosae</i> parasitizing <i>Sombucus nigra</i> is a fungus new to the Mycota of Poland. <i>Ampelomyces quisqualis</i> was found associated with <i>Mirosphaera symphoricarpi</i> colonizing <i>Symphoricarpos albus</i> and with <i>Sphaerotheca mors-uvae</i> parasitizing <i>Ribes nigrum</i>; these powdery mildew fungi are fungal hosts of <i>A. qulsqualis</i> not recorded in the literature to date.