Three hypersensitive resistant, six partially resistant (slow rusting), and one susceptible spring bread wheat (Triticum aestivum L.) cultivars were evaluated for grain yield, test weight, and kernel weight under artificially created epiphytotics of leaf rust disease (caused by Puccinia recondita f. sp. tritici) with and without fungicide protection for three years. Rusted plot yields were 4 percent lower compared to fungicide-protected plot yields for cultivars with hypersensitive resistance. In rusted plots, grain yield and kernel weight averaged 8 percent less for cultivars with partial resistance but varied from 2 to 20 percent less depending on cultivar. The susceptible check cultivar, Yecora 70, averaged 27 percent lower grain yield, 22 percent lower kernel weight, and 6 percent lower test weight in rusted plots. Slight reduction in test weight was also observed for each cultivar. Losses in grain yield could, therefore, be reduced to levels similar to those of hypersensitive resistant cultivars by the use of partial resistance. We discuss the sustainability of partial genetic resistance to leaf rust. Since partial resistance is expected to be durable, and since rust levels and effects on yield in farmers' fields are likely to be less than in this experimental plot study, partial resistance should give long-lasting resistance at a negligible cost in yield that is insufficient to justify the use of fungicides.