Examination of pitching yeasts from various breweries by the method involving plating on an agar medium containing lysine, revealed the presence, in most samples, of “wild yeasts” in the proportion of about one cell per million cells of pitching yeast. Whereas many of the “wild yeasts” belonged to species previously recorded from this source and from spoiled beer, others do not appear to have been noted before in brewer's yeast. Pichia membranaefaciens, Candida myeoderma, Toruloptis colllculosa and Torulopsh Inconspieua were of common occurrence, and a total of thirteen other species was observed on different occasions.