Three corn root bioassays were evaluated for detecting imazaquin in soil. Two techniques, one which utilized a cone-shaped tube as the growth container and another, a petri dish, were compared to a method that utilized a thin layer of soil between two 20 by 20 cm glass plates. Corn root growth responded logarithmically to imazaquin regardless of bioassay method. Corn was most sensitive to low imazaquin concentrations when grown using the glass plate apparatus. At a low concentration (0.5 ng/g) of imazaquin, corn root length was reduced 6% using the cone-tube, 2% using the petri dish, and 24% using the glass plate method. In contrast, the cone-tube method provided a better measure of high imazaquin concentration (200 ng/g) than the other methods.