Fueled by the fast-growing DNA sequence information, proteomics-the large-scale analysis of proteins-has become one of the most important disciplines to characterize protein activities and provide insight into functional network between protein molecules in a high-throughput format. More and more evidence has pointed out that proteins rarely act as single isolated species when performing their functions in vivo; they normally associate with other proteins and/or molecules as complexes and function in a network mode. The goal of my laboratory is to discover and characterize the activities of large collection of proteins or an entire proteome as the first step in better understanding the mechanisms of biological processes. More specifically, the lab is interested in analyzing protein posttranslational modifications, various signaling network, protein profiling, and host-pathogen interactions on the proteomics level. It is obvious that this type of research requires high-throughput technologies suited for proteomics studies. We have developed two key technologies to address the above challenges. We have achieved to express and purify large numbers of proteins from both prokaryotic and eukaryotic systems and build high-density protein microarrays for various organisms in various array formats. We have shown that protein chips can serve as a versatile tool to study protein-protein, protein-nucleic acid, protein-lipid, enzyme-substrate, and protein-drug interactions. In addition, protein posttranslational modifications can also be characterized in a chip format. Although this technology is still in its infancy, we believe that it can be applied to higher eukaryotes in the near future.