Pythium nodosum sp. nov. has been isolated from a soil sample taken in the Burgundy region in France. The fungus has spherical to variously shaped proliferating sporangia, smooth-walled oogonia which are crowded with different antheridial branches making a complicated knot around the former, and aplerotic oospores. Morphological and reproductive aspects of Pythium nodosum as well as the PCR of the internal transcribed spacer (ITS1) of the ribosomal nuclear DNA coupled with restriction fragment length polymorphism analysis are described here. The nucleotide sequences of ITS1 encoding 5.8S rRNA is also given.