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