Estimates of the nuclear DNA (nDNA) content in the yeast cells of 43 strains of Leucosporidium scottii, Rhodosporidium toruloides, and related yeast taxa were analyzed by fluorescence microscope photometry. Quantitative differences of nDNA contents occur among 18 strains of L. scottii. Four groups of strains with similar nDNA content were recognizable in L. scottii. One group contained only one strain (IFO 9474) which was characterized by the Q-7 system. The respective strains of the remaining three groups had either Q-9 or Q-10 as the major ubiquinone system, except CBS 8188 having both of these. Some mating strains of L. scottii had almost twice the amount of nDNA as the presumed haploid value. In contrast, both mating type A and a strains of R. toruloides had nearly identical average nDNA contents. Our results suggest the presence of aneuploidy among yeast cells of L. scottii.