Soybeans and other crops have been improved genetically for many decades throughtraditional crop breeding ? a technique that requires that species be sexually compatible.With the development of biotechnology methods, scientists have the ability to transfersingle genes from one living organism into another, regardless of species or sexualcompatibility. Varieties that are developed through the transfer of genes between speciesthat are not sexually compatible are referred to as 'transgenic.'Transgenic soybean plants have been developed with a gene from a soil bacteria thatallows the use of an herbicide that would normally kill soybeans. Transgenic soybeanvarieties have been adopted rapidly by U.S. growers (Table 1). Transgenic soybeanacreage represents approximately 60 % of the total acreage planted to transgenic cropsgrown in the U.S. (Corn and cotton are the other major crops with transgenic varietyplantings in the U.S.)Farmers are planting transgenic soybeans in the U.S. because of the weed control benefitsthat result from the use of an herbicide that damages conventional varieties. Thisherbicide, glyphosate (trade name 'Roundup') is a cost effective solution to many of theweed problems that U.S. soybean growers must overcome every year. The herbicidetolerant transgenic soybean is referred to as 'Roundup Ready.' The purpose of thisreport is to describe and quantify the weed control benefits provided on soybean acreageplanted with the transgenic varieties in 1998.