Competitive interactions of four spring bread wheat cultivars ( Triticum aestivum check for this species in other resources L.) with four wild oat ( Avena fatua check for this species in other resources L.) seedling densities were assessed in field studies in southeastern Ethiopia during three cropping seasons (1991-93). Grain yield of wheat was linearly proportional to the seedling density of wild oats, but yield reductions at the maximum density of 90 weed seedlings m-2 ranged from 26 to 63% across the wheat cultivars. The semidwarf cultivar Dashen was the most sensitive to wild oat competition, while the intermediate height cultivar Enkoy was the least affected. Wheat cultivars varied markedly in their ability to suppress A. fatua tillering and seed production, differentially affecting wild oat seed and straw yield, panicle production, seed number panicle-1, and thousand kernel weight. Given the limited access of Ethiopian peasant farmers to grass herbicides, wheat breeders should be encouraged to exploit such variability, and develop germplasm with a greater inherent ability to compete with wild oats.