This report attempts to identify the contributions of technology and weather to soybean yield variation for the period 1965 to 1979 in the Corn Belt Region. Technology variables included were genetic improvement, herbicides, and row-width. A pooled cross-sectional time-series data base was used to estimate regression parameters for herbicides and other variables. A marginal private benefit/cost return of $2.3 per dollar of herbicide cost was estimated for additional land treated with herbicides.