Among the lower fungi parasitism is widespread. One of the most commonly affected objects is microscopic algae. Interaction in the system “host-parasite” are poorly understood, both in natural conditions and in culture. Rhizophydium mammilatum – parasite yellow-green alga Tribonema gayanum is one of the most common chytrid fungi in the North-West of the Russian Federation. The ability to detect, and elimination of the parasite gives us an idea of its distribution in nature. Culturing the parasite in the binary culture “host-parasite” gives the prospects of using these objects as a model system for studying aspects of parasitism of microscopic eukaryotes.