The Germplasm Resources Information Network (GRIN), the master database of the National Plant Germplasm System, was queried to measure the usefulness and limitations of ex situ germplasm collections for prairie research. A list of 862 taxa of grasses and forbs native to the prairies of the midwestern United States was checked in a stepwise fashion against recognized names in the GRIN database. Each species was checked against recognized names in the taxonomy area of the database. For each recognized species, the accessions area was queried to see if any populations were entered in the database. The inventory area was then searched to learn if samples of these populations were available for free distribution to researchers and to determine which site is responsible for the maintenance of each available population. Populations of 146 taxa of prairie plants were represented in the GRIN database. Another major ex situ source of prairie plant germplasm was not accessible through the GRIN database. The USDA Soil Conservation Service Plant Materials Centers evaluate native species for their potential use in conservation and windbreak plantings. The holdings of the Plant Materials Centers and other institutions not yet part of the GRIN database are briefly discussed.