Bromus diandrusRoth, is one of the most troublesome weeds in spring wheat crops of the western Cape wheat producing area of the Republic of South Africa and Australia. The selective control of this weed in wheat crops may, in future, be possible with MON 37532 (sulfosulfuron) a new herbicide developed by Monsanto SA. The effect of the relative density ofB. diandrusin a wheat crop on the efficacy of this herbicide sprayed at either the 2- or6-leaf stage of the weed was studied in a pot experiment in a temperature-controlled glasshouse. A density of 3 plants pot-1(170 plants rrr-2) was used for the wheat crop, while that ofB. diandrusvaried between 0 and 10 plants pot-1(565 plants-2). At early applications (2-leaf stage), efficacy of MON 37532 improved with higher densities ofB. diandrus.This was possibly due to stress conditions created by higher weed densities. This tendency was less evident when MON 37532 was applied at the 6-leaf stage. Reduced susceptibility in the older plants and less efficient wetting of weeds in pots with high weed densities were probably the reason for reduced percentage control when plants were sprayed at this stage.