Formation of 14C-atrazine degradation products and their distribution in the top 90 cm of soil was determined over 16 mo in a Webster clay loam in the field. After 16 mo, 64% of the applied 14C could still be accounted for in the 90-cm soil profile. At 1 mo after treatment (MAT), 14C moved to the 70- to 80-cm depth. Rapid movement of radioactivity could be attributed in part to preferential movement through vertical macropores. Atrazine accounted for 32% of the 14C applied 16 MAT and was the predominant 14C-compound in soil below 10 cm through 12 MAT. Hydroxyatrazine (HA) was the major degradation product in the top 10 cm of soil accounting for 9% of the 14C present 1 MAT and increasing to 24% within 6 MAT. Deethylatrazine (BEA) was the predominant degradation product at depths greater than 10 cm, accounting for 26% of the 14C in the 10- to 20-cm depth 16 MAT. Deisopropylatrazine (DIA) accounted for less than 10% of the 14C recovered at any soil depth. Deethyldeisopropylatrazine (DEDIA) and an unidentified product were detected in soil extracts 1 MAT indicating further degradation past primary metabolites. The proportion of DEA and DIA increased while the proportion of HA decreased as soil depth increased indicating that DEA and DIA are more mobile in soil than HA. The large amount of radioactivity remaining in the soil 16 MAT suggests that a large pool of atrazine and its degradation products are present in the soil for a long period of time, having the potential to move deeper in the soil and ultimately contaminate ground water.