No repression of the synthesis of respiration enzymes was found in the petite--negative yeast Endomyces magnusii under the action of high concentrations of a fermented sugar in the growth medium. Transfer of the cells from 0.3% to 5% sucrose (or glucose) did not result in a decrease in their respiration activity or molar content of cytochromes a+a3 (components of the respiratory chain most sensitive to the glucose repression in other yeast species). The respiration of intact cells grown on 5% sucrose (glucose) was inhibited by 80--94% with cyanide and by 90--98% with cyanide plus salicyl hydroxamate. These data indicate that mitochondria play a predominant role in the oxidative activity of cells. Mitochondria from cells grown on 5% sucrose (glucose) hardly differ in their metabolic activity, effectiveness of oxidative phosphorylation, coupling, and regulation of the metabolic state from mitochondria isolated from completely derepressed cells (the stationary state from mitochondria isolated from completely derepressed cells (the stationary phase of growth, complete exhaustion of the substrate in the course of growth in a medium containing 0.6% sucrose).