Indigenous fresh water fish species were collected in all of the major watersheds in Massachusetts during the summers of 1965, 1966, and 1967 and an individual analysis of these fish conducted to determine the concentrations of DDT and metabolites, DDE and DDD (TDE). In all, 1,310 individual fish specimens were collected and analyzed from 93 stations. Mean DDT concentrations based on the analysis of five fish per station ranged from 0.17 to 28.88 parts per million. A study of factors relating to the concentration of pesticide by fish showed that some fish species had varying abilities to concentrate DDT. Results of this study are expressed in parts per million of pesticide found in whole fish and based on dry weight. Conversion factors to convert parts per million based on dry weight to parts per million based on wet weight were determined for nine species of fish. (Author)