Dominant drug resistance markers offer experimental flexibility in the study of Saccharomyces cerevisiae by eliminating the dependence on auxotrophic mutations and, because they are phenotypically neutral, avoid the deleterious effects of auxotrophic mutations. We have developed a new dominant resistance marker, dsdAMX4, for use in the genetic manipulation of S. cerevisiae. The dsdA gene, which is derived from Escherichia coli and encodes a D-serine deaminase, confers to S. cerevisiae resistance to D-serine and the ability to use D-serine as a nitrogen source. Here we describe the construction of a dsdAMX4 cassette, capable of expression in S. cerevisiae, and the characterization of this new marker for use in chromosomal gene disruption. The unique selection properties of the dsdAMX4 cassette make it an important addition to the existing array of S. cerevisiae genetic tools.