Until the first isolation of Kloeckera sp. No. 2201 as a methanol-utilizing yeast in 1969 by Ogata et al., 1 no eukaryote was recognized to be able to grow on reduced C,-compounds, e.g., methane and methanol, as the sole source of carbon and energy. In 1948, Wickerham and Burton 2 classified methanol to a group of compounds, which were not utilized by yeast, through the test for the carbon assimilation with 100 strains of yeast representing 22 genera. Since then, methanol had been neglected as a possible growth substrate for yeasts. Recovery of yeasts from the culture broth is significantly easier and cheaper than that of bacteria due to the larger diameter of the yeast cell. As single-cell protein, yeast is psychologically more acceptable for human consumption because of the experience of using the cells as a food supplement. For these reasons, investigations on methanol-utilizing yeasts have attracted much attention in applied and fundamental fields of microbiology during these 1½ decades. 3 - 6