Mutanase (Mutanase Novo) affects the high frequency production of protoplasts in the following strains of yeas Saccharomyces cerevisiae, Schizosaccharomyces pombe, Kluyveromyces lactis, Trichosporon pullulans, and Schwanniomyce alluvius. Regeneration frequencies varied with the strain used and ranged between 10 and 18%. This enzyme preparation appear to be a very useful means of obtaining protoplasts from a wide variety of yeasts currently being used for experimental purposes