Addition of beta-mercaptoethanol at a concentration of 2-3 mM to media containing methanol, glucose, or yeast extract caused a 50% inhibition of the growth of wild-type yeast Pichia methanolica; mercaptoethanol at a concentration of 0.7 to 25 mM inhibited the growth of the mutant strain ecr1. The mutation mth1 of P. methanolica repressed its ability to consume methanol and was accompanied by the loss of alcohol oxidase (EC 1.1.3.13) activity. beta-Mercaptoethanol restored the ability of mth1 mutant cells to grow on methanol and stimulated their growth under derepression conditions. The growth effect of beta-mercaptoethanol during derepression was accompanied by partial restoration of alcohol oxidase activity.