The reductive dechlorination of three dichlorophenol (DCP isomers was studied in anoxic sediments collected every other month for a year from five sites in one pond. Several physical, chemical and microbiological characteristics of the sediments also were determined to identify correlations with DCP dechlorination that may be used to predict the persistence of these compounds in anoxic sediments. Stepwise regression indicated that for 2,5- and 3,4-DCP, sediment pH, redox potential (Eh), and concentration of sulfate and nitrate accounted for 83% of the variation in T(sub 50) values (time for dechlorination of 50% of a DCP to a monochlorophenol). Although the number of sediment microorganisms that dechlorinate 2,4-DCP varied two orders of magnitude in sediments collected during the study year, regression analysis indicated that neither this nor any other variable could account for greater than 50% of the variation in T(sub 50) values for 2,4-DCP. Chlorine was removed preferentially from the aromatic ring in the order ortho>para>meta; however, the influence of chlorine position on the ring on the persistence of the DCPs was generally not statistically significant.