Protoplasts of petites of strains 625-C(I) of Saccharomyces diastaticus and NCYC 1085 of Saccharomyces cerevisiae, originally obtained from the National Collection of Yeast Cultures, England, were fused with protoplasts of Candida pseudotropicalis, Saccharomyces rosei, Yaccharbmycesmontanus, Pichiamembranefaciens, Hansenula anomala, Hansenula capsulata, and Schizosac-charomyces pombe. The respiratory-competent products of the fusions were selected on the basis of using at least one of the carbon sources utilized by the petite parent and not by the other. The products of the fusion of C. pseudotropicalis x 1085(p(-)) consisted of two cell types; an oval cell which utilized both lactose and maltose and fermented lactose vigorously, and a cylindrical form which fermented maltose slowly. The S. rosei x 1085(p(-)) hybrids had acquired the ability to metabolize and ferment galactose, and to ferment maltose, from the petite parent. The P. membranaefaciens x 625(p(-)) hybrids acquired the ability to metabolize galactose, sucrose and maltose, but fermented only glucose, weakly, like the P. membranaefaciens parent strain. The H. capsulate x 625(p(-)) hybrids, unlike the hybrids with P. membranaefaciens or S. rosei, resembled the petite parent morphologically and also had the fermentative abilities of this strain (galactose, maltose, sucrose and starch), and the ability to ferment starch was considerably enhanced. The S. montanus x 625(p(-)) hybrids acquired the ability to utilize starch. Schizosaccharomyces pombe x 625(p(-)) hybrids resembled S. pombe morphologically, but had the ability to metabolize galactose and starch. Some of the asci produced by these hybrids contained abnormal numbers of spores. H. anomala x 624 x(p(-)) hybrids fermented starch, though weakly.