Genetic structure of populations ofHordeum spontaneum, the wild progenitor of barley, was studied electropho-retically in proteins encoded by 28 gene loci in 1179 individuals representing 28 populations covering the entire ecological range in Israel; for comparison, the same test was conducted in 100 random seeds of Composite Cross XXI (generation 17) of cultivated barley,Hordeum vulgare. The results indicate that: a)H. spontaneum in Israel is genetically highly polymorphic, b) clinal, regional and local genetic patterns are significantly correlated with and predictable by climatic and soil variables, suggesting the operation of natural selection, and c) natural populations are on the average more variable than the tested Composite Cross generation. This genetic variation awaits testing and exploitation in breeding programs.