Under the action of elevated temperature (37 degrees C), wine yeasts sported thermotolerant variants with respiration deficiency and increased fermentative function. The activity of dehydrogenase in the variants was also low. The sediment of Saccharomyces vini cells became dust-like instead of flocculent at 37 degrees C. The giant colonies of the variants were more compact and smalled cf. the parent cultures, and their radial plication was less pronounced. The morphological and physiological properties of the thermotolerant yeast variants were preserved during cultivation at 37 degrees C for many years (greater than 10) or at 27 degrees C for several months (greater than 6).