In a specially bred series of Saccharomyces-strains of different ploidy (haploid to tetraploid) the content of DNA, RNA, folic acid, niacin, pantothenic acid, thiamine, and catalase has been determined. The cell content of these substances increased nearly proportional with increasing ploidy. Diploid strains, however, which were heterozygous for only the mating type alleles proved to have a remarkable higher cell content of DNA, catalase and undigested folic acid than diploid strains homozygous for the mating type alleles. Generally those strains, which are able to sporulate, proved to have a higher content of the last mentioned substances per dry weight than those which are able to mate. These latter results are an interesting biochemical parallele to the remarkable resistance of diploid aα-strains to ionizing radiations.