AbstractHybridization was shown to occur both between strains of the imperfect diploid yeast Candida albicans and between C. albicans and the distantly related hapoid yeast Candida (Pichia)guilliermondii Protorophic hybrids were selected from croses of multiply marked auxotropic mutants two species. In most cases, mild ultraviolet irradiation of the C. albicans partmer was reqiured.Examination of auxotropic markers in segregants from the hybrid indicated that recombination, rather than the heterokaryon, formation, had occured in these croses. The DNA content of the hybrids varied from diploid or aneuploid (for crosses between C. albicans and C. guilliermodii) to triploid (for C. albicabs × C. albicans). It seems possible that genetic exchange analogous to this may occur in nature.