The utilization of lysine for growth by each of some 180-odd yeast species and strains has been examined in a synthetic medium containing L-(+)-lysine as the sole source of nitrogen. It was found that, whereas none of the strains of brewery top yeast (Saccharomyces cerevisiae) or bottom yeast (Sacch. carlsbergensis) examined utilized lysine under the experimental conditions, many other yeasts, including a number of brewery wild yeasts, did so and gave moderate to good growth in the medium. On the basis of these findings, it is suggested that the described medium is of potential value as an enrichment medium for the detection and isolation of a wide range of foreign yeasts in brewery pitching yeasts.