The herbicide atrazine was applied pre-emergence to corn plots which were drained by separate drains (average depth 70 cm). Water samples were collected from the tile outlets, extracted with chloroform, and the atrazine content determined by gas chromatography. The discharge of atrazine residues monitored over a 4-yr period ranged from 2.75 to 8.69 g/ha annually. The concentration varied between 0.5 and 3.50 μg/liter of water. Losses of atrazine were greater from plots under a continuous corn crop and a high fertility level than from plots under rotation corn and low fertility.