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The objective was to quantify leaching of the widely used low-dosage sulfonylurea herbicides rimsulfuron and its primary degradation products IN70941 ([N-(4,6-dimethoxypyrimidin-2-yl)-N-((3-ethylsulfonyl)-2-pyridinyl)urea]) and IN70942 ([N-((3-ethylsulfonyl)-2-pyridinyl)-4,6-dimethoxy-2-pyrimidineamine]) at two sandy research fields in Denmark. Water was sampled monthly from the vadose and groundwater zones at the two sites (Tylstrup and Jyndevad) over a 4–6-year period following application of rimsulfuron. No rimsulfuron was detected in the water samples. At the Jyndevad site, IN70941 was detected in the vadose zone at a depth of 1m for as long as three years in annual average concentrations exceeding the EU limit value for drinking water of 0.1μgL⁻¹. At the Tylstrup site, IN70941 was detected at a depth of 2m in concentrations just below 0.1μgL⁻¹. The groundwater concentration of IN70941 …