This study was undertaken to estimate the economic impact of efforts since 1973 by the International Maize and Wheat Improvement Center (CIMMYT) to develop spring bread wheat varieties resistant to leaf rust caused by Puccinia triticina. This wheat disease is of major historical and economic importance worldwide. The challenge in estimating the benefits lies in the pathogen’s ability to mutate to new races, which may infect previously resistant varieties. Thus, whereas productivity enhancement is often measured in terms of yield gains and increased supply, productivity maintenance is measured in terms of the yield losses avoided through resistance. An economic surplus approach adjusted for maintenance research and a capital investment analysis were applied to estimate the returns on CIMMYT’s investment. The results of the analysis suggest an internal rate of return of 41%. When discounted by 5%, the net present value was 5.36 billion 1990 US$, and the benefit-cost ratio 27:1. This implies that every 1990 US dollar invested in CIMMYT’s wheat genetic improvement over 40 years has generated at least 27 times its value in benefits from leaf rust resistance breeding in spring bread wheat alone. The findings of the study emphasize the importance of maintenance research in crop breeding programs.