ABSTRACT: Organochlorine contaminants, including polychlorinated biphenyls (PCBs), chlorinated bornanes (CHBs), dichloro-diphenyl-trichloroethanes (DDTs), chlordanes (CHLORs), hexachlorocyclohexanes (HCHs) and, chlorobenzenes (CBZs) were quantified in 188harbour porpoises (Phocoena phocoena) killed in commercial fisheries in the coastal waters of the Avalon Peninsula, Newfoundland (n = 29), the Gaspé Peninsula, Quebec (Gulf of St. Lawrence) (n = 58), Grand Manan Island, New Brunswick (Bay ofFundy) (n = 86), and Jeffreys Ledge in the Gulf of Maine (n = 15). Levels were compared to determine if there were systematic differences in the organochlorine (OC) contaminant composition of harbour porpoises from these areas (Newfoundland, St. Lawrence,Bay of Fundy-Gulf of Maine) in the western North Atlantic. Bivariate analyses run on all 188 individuals showed both Fundy-Maine and St. Lawrence males had significantly higher levels of CHLORs, DDTs, PCBs and CHBs than Newfoundland males. Fundy-Mainemales also had significantly higher levels of CHLORs and PCBs than those from the St. Lawrence and St. Lawrence males had significantly higher levels of HCHs than males from Fundy-Maine. Females from Fundy-Maine had significantly higher levels of totalPCB than both St. Lawrence and Newfoundland females. Total DDT levels were significantly higher in Fundy-Maine and St. Lawrence females than those from Newfoundland. Total CHLOR values were significantly higher in Fundy-Maine than in Newfoundland females.Multivariate analysis, run on a subset consisting of 100 immature harbour porpoises showed significant differences among the group centroids on both discriminant functions (Wilks' Lambda; p < 0.001) demonstrating that these geographic groups aredistinguishable based on OC levels. These results indicate that delineating the western North Atlantic harbour porpoise population into sub-populations defined as Newfoundland, Gulf of St. Lawrence and Bay of Fundy-Gulf of Maine is appropriate.