In 1994, herbicide efficacy and competitive index databases were adjusted in the soybean herbicide recommendation program HERB to best reflect data for Mississippi. Field experiments were conducted to compare efficacy and economics of postemergence herbicides recommended by HERB and MSU-HERB. The study was conducted utilizing four locations over 2 yr, which provided different soil types, weed spectra, and environmental conditions with which to evaluate weed control from herbicides recommended by these programs. HERB and MSU-HERB agreed on an herbicide recommendation in 62% of the modeling runs. Herbicides recommended by both software versions were generally effective for controlling the predominant weed species at each location. In instances where there was a significant difference in herbicide efficacy between herbicides recommended by HERB and MSU-HERB, improved weed control resulted from herbicides recommended by MSU-HERB. In 1994, excellent moisture conditions enabled soybean to gain a significant competitive advantage over weeds and, as a result, yield loss predictions after treatment were overestimated in most instances. Conversely, 1995 environmental conditions better represented average Mississippi growing conditions, and yield loss predictions after treatment were more accurate. Yield loss prediction accuracy of HERB versions was related to the length of interference between soybean and weeds. Thus, prediction accuracy of HERB and MSU-HERB was similar. Soybean yield increase and net economic gain following MSU-HERB recommendations was as high or higher than following HERB recommendations.