Reaction Biology Corporation (Malvern PA) has developed homogeneous-phase reaction microarrays to serve the NIH Roadmap initiative for nanoliter-scale biochemical high throughput screening (HTS) in drug discovery, large scale IC50 determinations, and selectivity profiling. These nanoliter reactions are 1000 to 10,000-fold smaller than well plate formats currently in use. Preliminary data is presented for microarray HTS against serine proteases, caspases, MMPs, tyrosine kinases, and serine/threonine kinases. Aim 1: A chemical microarrayer will be designed and built through a Consortium with TeleChem (Sunnyvale CA). This microplate arrayer will deploy a 384-pin manifold to print NIH library compounds to array-plates containing up to 38,400 compounds per glass array-plate (SBS standard). The design goal for this instrumentation is to achieve the printing of 10 sets of the entire NIH repository in a 24-hr print run to be used for 10 individual HTS campaigns (5 million reactions). Aim 2: An array-plate activator will be designed and validated for the rapid delivery of sub-nanoliter quantities of enzymes, substrates, cofactors, and detectors to the compound array-plates. The design goal for this instrumentation will be to initiate biochemical screens against the entire NIH compound repository (20 array-plates containing 500,000 compounds) in 30 minutes. Aim 3: Construction and delivery of an array-plate activator beta-unit to the NIH for testing and validation. This instrumentation seeks to exploit the tremendous liquid handling power of microarrayers, the miniaturization of microarrays for compound conservation and easy HTS assay development, and the resolution/sensitivity of multicolor laser scanners. Other applications are enabled by this instrumentation: (1) the rapid printing of large chemical libraries on plates pre-coated with an immobilized protein and binding partner would facilitate protein-protein inhibition HTS;(2) the ability to rapidly print 100,000 or more cellular lysates produced in well plate HTS facilitates highly multiplexed detection of numerous intracellular antigens by reverse phase arrays analyzed by sandwich ELISA. Overall, this instrumentation allows a large number of wild type or recombinant protein targets, each obtained in miniscule quantity, to be screened against 100,000 to 500,000 compounds of the NIH repository.