Exploring the interactions among the proteins identified by genome sequencing can be overwhelming. Like a visitor arriving in a new country, there are many different ways to take in the points of interest. In the pregenomic era, we tended to stay in particular neighborhoods and study them in great detail. By analogy, we've learned a lot about protein–protein interactions from studying specific proteins or biochemical activities from many model organisms. Complete genome sequences have whetted our appetite for a different kind of exploring by giving us the genes for every protein encoded by the genome. Now we can complement our knowledge of the famous landmarks with a directory of every building. Recent papers from Uetz et al. (1) and Ito et al. (2) have described the early progress at generating a comprehensive census of the protein–protein interactions from the budding yeast Saccharomyces cerevisiae. These two groups both used the yeast two-hybrid system (3) as a rapid and generalizable assay to detect interactions between any two proteins, called the bait and the prey. Pairwise combinations of proteins were examined where a full-length ORF of every known or predicted gene from S. cerevisiae was used as bait and/or prey.