We report the construction of Saccharomyces cerevisiae strains isogenic to W303-1a that are designed to allow efficient genetic analysis. To facilitate the generation of null alleles of target genes by PCR-mediated gene disruption, we constructed designer deletion alleles of the ARG4, TRP1 and URA3 genes. In addition, a single pair of oligonucleotide primers were designed that can be used to amplify any of several marker genes for use in PCR-mediated gene disruption. A new version of the 'reusable' hisG-URA3-hisG cassette was constructed for use in PCR-mediated gene disruption. Finally, to facilitate the formation of isogenic diploids by selection, we constructed strains that contain combinations of wild-type alleles of ADE2, HIS3, LEU2, TRP1 and URA3.