The use of herbicides is increasing rapidly year by year. 2,4-Dichlorophenoxyacetic acid (2,4-D) is the most widely used of the herbicides offered on the market. Although 2,4-D was one of the first selective herbicides discovered and has been investigated by many workers over the years, there are still many questions concerning its metabolism. Hydroxylated derivatives have been found in some microorganisms and plants . This might be expected as hydroxylation is a prime method of detoxication in biological systems. 2,4-D has been found to be hydroxylated predominantly in the 5-position. However, 4- hydroxy-2,3- and 4-hydroxy-2,5-dichlorophenoxyacetic acids have been identified in some cases. This is interesting as it involves much more elaborate mechanisms than hydroxylation in a vacant position. The formation of these hydroxy acids requires a chlorine shift to one of the meta positions and hydroxylation in the para position. The object of this work is to determine whether hydroxylated derivatives are formed by excised roots from 2,4-D or related herbicides. Some workers have also found muconic acids and gamma-lactones as succeeding stages in the metabolism of these herbicides. This would follow from an oxidative degradation of the ring structure. The lactones found are of interest from the public health standpoint. The gamma-lactones isolated contain double bonds in the even numbered positions and compounds of this type have been found to be carcinogenic. If these compounds appear in any appreciable amounts and are not very transitory in nature, the use of the herbicides involved might require reevaluation by regulating organizations.