This report provides preliminary data for Madison Limestone test well 3 in Yellowstone County, Mont., including test-well history , geology of the test well, hydrologic testing, and geochemistry. It also discusses the preliminary results and future testing. The test well was drilled as part of the study to determine the water-resource potential of the Madison Limestone and associated rocks to meet future water needs in a 188,000-square-mile region that includes the coal-rich area of the Northern Great Plains. Drilling and testing were designed to yield a maximum of stratigraphic, structural, geophysical, and hydrologic information. (Woodard-USGS)