In the past, studies of protein activities have focused on studying a single protein at a time, which is often time-consuming and expensive. Recently, with the sequencing of entire genomes, large-scale proteome analysis has begun. Arrays of proteins have been used for the determination of subcellular localization, analysis of protein-protein interactions and biochemical analysis of protein function. New protein-microarray technologies have been introduced that enable the high-throughput analysis of protein activities. These have the potential to revolutionize the analysis of entire proteomes.