Twenty-four field experiments were conducted between 2005-2007 in Ontario and the United States to evaluate the effects of simulated drift followed by registered in-crop herbicides on corn and soybean. In corn, simulated glyphosate drift (200 g ai/ha) resulted in visual injury and a decrease in height, dry weight, stand count and yield. Simulated glyphosate drift followed by in-crop herbicides resulted in an additive response for all variables analyzed. In soybean, as the rate of simulated mesotrione or dicamba/diflufenzopyr drift increased, injury increased and dry weight, height and yield decreased. Simulated mesotrione drift followed by bentazon resulted in negative synergistic responses in respect to injury and additive responses in respect to yield. In contrast, antagonistic responses were observed when imazethapyr or glyphosate plus chlorimuron-ethyl were applied after simulated mesotrione drift. A negative synergistic yield response was observed with simulated dicamba/diflufenzopyr drift followed by chlorimuron-ethyl but not when followed by either imazethapyr or bentazon.