Despite the improvements in linkage techniques introduced by PRC and mircrosatellites, genotyping remains very technical, time consuming and expensive. Multiplexing the analysis is one way to reduce the cost and improve the efficiency. We propose to develop, produce and distribute microsatellite markers suitable for multiplex analysis on automated hardware. We currently produce and distribute over 3,000 microsatellite markers to over 100 labs for the analysis of linkage in human, mouse and rat. These are typically analyzed using 32p, autoradiograms and manual scoring. Many of these markers run under poorly defined PCR conditions further complicating the procedure. The proposed markers would allow nono-isotopic, automated detection, multiple marker per lane and would all run under validate PCR conditions. This would be achieved by the redesign of primer sequences where necessary, carefully selecting well space markers with allele size ranges that would allow multiple markers per lane, and multicolored fluorescent labeling which would further increase the number of markers per lane. Marker set with 10 cM resolution in human would be the objective of phase II.