A wealth of resistant plants was found in the tetraploid wild oat Avena barbata Pott, as well as in the hexaploid A. sterilis L. The appreciably high frequency of resistance found in A. sterilis (about 7.5%) reveals an abundant and useful source of resistance, for direct crosses with cultivated varieties. The most efficient procedure of seed collection and screening for obtaining sources of resistance, was (1) random sampling of small samples in the entire region (method A); (2) seedling tests in the greenhouse; (3) construction of distribution maps of resistance; (4) more intensive search in promising locations according to distribution maps (methods B and D). The use of seedling resistance as an indication of adult resistance may result in overlooking the adult plant resistance in up to 40% of the locations where adult resistance could have been found by direct adult tests. Nevertheless, the frequency of locations where plants were found to be resistant in both seedling and adult stages allows for the more convenient use of seedling tests in initial screening.