Studies of yeasts in various ecological niches in Ukraine have been carried out in the Institute of Microbiology and Virology NASU from the beginning of the 1960s. The studies examine biological features of yeasts in nature and the laboratory, and the qualitative and quantitative effects of ecological conditions on their populations. A major aspect of the work is the selection of strains of these economically important microorganisms. Results show that yeasts are widespread from natural and industrial sources including rhizospheres and phyllospheres of wild and cultivated plants, various soils, fresh water, cold-blooded and warm-blooded animals including man, and in materials used for wine, sugar and milk production. Abundance and species composition depend on source of isolation. New methods are proposed for isolating yeasts from various niches. Yeasts are a source of useful probiotics, and can be used to produce albumen supplements for human and animal food, and vitamins, carotenoids, organic acids, aminoacids, enzymes, lipids, and extra-cellular polysaccharides from the following substrata: n-alcans, hydrolyzed raw plant material, sulphite alkali, milk serum, ethanol and methanol. Killer-yeasts, and yeasts which are neutral or sensitive to killers are also isolated from natural sources. A collection of yeasts based on the isolated strains is maintained as part of the Ukrainian National Collection of Microorganisms.