A method for hybridization of yeast protoplasts ofSaccharomyces cerevisiae andCandida holmii by electrofusion was optimized. The hybrids were screened on maltose-acetate agar plates. The average fusion frequency was 1.1xl0-3. Two hybrids of 132 collected from selection plates were found to be stable over 15 sequential shake flask cultivations. However, the strains reverted during production of baker’s yeast in a laboratory scale process imitating the industrial process.