Potato is an important world crop with an abundant diversity of wild relatives for research and breeding. Over 100 tuber-bearing Solanum relatives of the cultivated potato occur naturally from southern Chile to the southwest United States. Only five of these have been reported in the United State s, and only two exist with certainty (S. stoloniferum/fendleri and S. jamesii). The authors and colleagues have conducted expeditions in the southwest United States each season since 1992, collecting over 200 new germplasm samples. This work has greatly improved the representation of these species in the genebank with respect to geography and genetic diversity available to germplasm users worldwide. Corrected or refined collection site information now makes it possible to easily find these typically small populations for continued in situ study and sampling. Collecting experiences, often in contrast with conventional wisdom, have been documented for the benefit of future collectors. A broader sampling of the region has allowed studies of the association of eco-geo parameters with patterns of genetic diversity in an attempt to predict ''hot spots'' of diversity for future expeditions. Evaluation of these materials has resulted in the discovery of new useful traits-novel mutants, disease and pest resistances, and human nutritional compounds.