Analysis of leachates from six U.S. municipal landfills revealed the presence of chlorinated 2-phenoxypropionic acid herbicides; however, none of the more widely used acetic acid analogues was present at quantifiable levels. All of the leachates contained Mecoprop (MCPP). 2,4-DP and Silvex were detected in four of the six. The herbicide 2,4-DB was also found in four of the leachates. These compounds persisted in the leachates during 2-3 years of storage while significant depletion of total organic carbon (TOC) in general and of low molecular weight carboxylic acids in particular was observed. Since landfills and leachates are microbially active environments (as demonstrated here by the TOC depletion during storage), this unexpected lack of degradation of several phenoxy herbicides poses concerns for possible groundwater contamination.