In the years 2001-2004, the occurrence of parasitic fungi of plants of the genera Betula and Salix growing in the Słowiński National Park was investigated. The plant species examined included B. pubescens, B. pendula, S. aurita, S. caprea, S. cinerea, S. fragilis, and S. repens. Plants of the genus Betula were affected by 9 species of parasiting fungi. In Poland, three of them (Microsphaera ornata var. europaea, Phyllactinia guttata, Melampsoridium betulinum) occur commonly, five (Asteroma leptothyrioides, Discula betulina, Fusicladium betulae, Phyllosticta betulina, Septoria betulina) are rare, and Septoria betulae-odoratae has not been recorded to date. Three species, Asteroma leptothyrioides, Fusicladium betulae, Phyllosticta betulina), were found on new plant hosts. Plants of the genus Salix were attacked by 8 species of parasiting fungi. Four of them (Melampsora allii-fragilis, M. caprearum, M. epitea, Uncinula adunca var. adunca) are common in Poland, four (Marssonina salicicola, Phyllosticta salicicola, Septoria salicicola, Trimmatostroma betulinum) rarely occur here. Uncinula adunca var. adunca, Marssonina salicicola, Phyllosticta salicicola, Septoria salicicola and Trimmatostroma betulinum were associated with the plant species not reported earlier to be their hosts.