The fate of [14C]deethylatrazine [2-chloro-4-amino-6-(isopropylamino)-s-triazine] was studied under controlled conditions by using undisturbed soil columns in the laboratory. In a 13-week leaching study, the percentage of [14C]deethylatrazine recovered was greatest in the first leaching event (1.3% of the applied 14C), suggesting that preferential flow occurred. The total concentration of deethylatrazine leached from soil columns over the 13-week period was 4.9 μg/L (3.6% of the applied 14C). Unidentified polar degradates made up 3.8% of the applied radioactivity recovered in the leachate, and didealkylatrazine [2-chloro-4,6-(diamino)-s-triazine] and deethylhydroxyatrazine [2-hydroxy-4-amino-6-(isopropylamino)-s-triazine] occurred in trace quantities. Sixty-seven percent of the applied 14C remained in the top 10 cm of soil columns, with 48% as bound residues, 12% as unidentified polar degradates, 5.5% as deethylatrazine, 0.2% as didealkylatrazine, and less than 0.1% as deethylhydroxyatrazine.