Chain- and ring-labeled 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) were supplied to corn by way of the nutrient solution. Autoradiographs of the paper chromatograms revealed that two identical C14-labeled metabolites were present in the extracts whether the plants were supplied with ring-or chain-labeled simazine. Corn, cotton, and soybeans all yielded appreciable amounts of C14O2 when grown in solutions containing chain-labeled simazine. One lb/A 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) (preemergence) caused a reduction in respiration as well as the activity of catalase, peroxidase, phenol oxidase, ascorbic acid oxidase, and glycolic acid oxidase in oats, soybeans, beans, cotton, peanuts, Johnsongrass, and corn, 7 and 11 days after treatment. Attempts to correlate enzyme activity with sensitivity to atrazine were unsuccessful, except that increasing phenol oxidase activity appeared to be roughly correlated with increasing resistance.