Bacteria have devised sophisticated His-Asp phosphorelay signaling systems for eliciting a variety of adaptive responses to their environment, which are generally referred to as the "two-component regulatory system." The widespread occurrence of the His-Asp phosphorelay signaling in both prokaryotes and eukaryotes implies that it is a powerful device for a wide variety of adaptive responses of cells to their environment. The two-component signal transducers contain one or more of three common and characteristic phosphotransfer signaling domains, named the "transmitter, receiver, and histidine-containing phosphotransfer (HPt) domains." The recently determined entire genomic sequence of Escherichia coli allowed us to compile systematically a complete list of genes encoding such two-component signal transduction proteins. The results of such an effort, made in this study, revealed that at least 62 open reading frames (ORFs) were identified as putative members of the two-component signal transducers in this single species. Among them, 32 were identified as response regulator and 23 were identified as orthodox sensory kinases. In addition, E. coli has five hybrid sensory kinases. The precise location of each ORF was mapped on a physical map of the entire E. coli genome. All of these ORFs were then compiled and annotated extensively.