The present paper begins a new series of studies investigating the occurrence of phytopathogenic micromycetes in Central Poland. Fungi of the orders Peronosporales and Erysiphalas are discussed in part one. Relevant knowledge on the subject is surveyed, and a list of published records (46 taxa) as well as the findings collected by the present authors (99 taxa) is provided. The list comprises 2 species new for biota of Poland - <i>Microsphaera deutziae</i> Bunkina and <i>Microsphaera elevata</i> Burrill, 10 rare and many common fungal species that had not been previously re00rded in this area as well as 21 plant taxa, mostly species of deliberate or accidental anthropogenic origin, that are new hosts of the parasites formerly listed in Poland.