With the complete sequence now available, the yeast genome project enters a post-sequencing phase that will concentrate on a comprehensive determination of gene function. Novel techniques have been developed to undertake genome-wide functional analysis at the levels of phenotype, transcript and protein. These include techniques for the efficient deletion of individual genes while tagging the deletants with specific oligonucleotide signatures, as well as strategies to quantify the physiological effects of such deletions by comparing growth rates and metabolite profiles under a range of conditions. Comprehensive approaches to the study of gene expression include hybridization array technology to identify and quantify transcripts, and the exploitation of mass spectometry to identify proteins resolved by two-dimensional gel electrophoresis. Yeast presents opportunities for the discovery of new human medicines both via the recognition of functional homologies between human and yeast genes and by the use of yeast to express human coding sequences specifying potential drug targets.