Using diploid strains of Saccharomyces cerevisiae and S. ellipsoideus, the following facts were found:Indole-3-acetic acid, 2,4-dichlorophenoxyacetic acid and α-naphthaleneacetic acid produced stable variants differing in the cell form and in the response to the actions of auxin to elongate cells, to induce respiration- deficient mutation and to promote sporulation.The auxins also produced stable variants differing in the ability to form spores.Acetic acid had no above-menthioned actions of auxin.Spore-formation and cell elongation of some of auxin-induced variants were controlled by auxin.Biological significance of the auxin-induced variation is discussed and the usefulness of some of these variants as experimental material for auxin physiology in general is pointed out.