Past experiences with long-term evaluations of woody landscape plants from Slovenia, Croatia, and Bosnia- Herzegovina in the north central United States indicated that a relatively low proportion of these introductions were well adapted to climatic and soil conditions. Based on these results, criteria were developed to focus future exploration for landscape trees and shrubs from more analogous environments in eastern and central Europe. Application of these criteria identified the forest– steppe transition zone in the northern half of Ukraine as a region with great potential, because of similarities to the north central United States in climatic extremes, soil types and natural plant communities. In 1999, the National Plant Germplasm System of the United States funded a collaborative seed-collection mission involving researchers from the United States Department of Agriculture, Michigan State University and the National Agricultural University of Ukraine. The exploration trip took place between 7 and 26 September 1999 and encompassed ca. 3200 km of travel to wooded sites through the forest–steppe transition zone. Eighty-nine seed collections, including 26 genera and 45 species of trees, shrubs and herbaceous perennials were obtained. The mission, its collections and conditions at collection sites are described in this report.