Lake whitefish, Coregonus clupeaformis, populations from across western Canada were studied in reference to their isolation and subsequent dispersal from separate glacial refugia. Frequencies of alleles of the genes governing electrophoretic phenotypes of glycerol-3-phosphate dehydrogenase (G-3-PDH), heart-type lactate dehydrogenase (LDH) and isocitrate dehydrogenase (IDH) proved useful for characterizing populations. Hemoglobin electrophoretic phenotypes and modal gillraker numbers for each population were useful in discerning differences among large groups of populations. Three biochemically distinct population groups of lake whitefish were found in western Canada and it is suggested that the most plausible hypothesis to account for the genetic integrity and geographical distribution of these groups is that they have separate origins in glacial refugia. Selection did not appear to account for the present genetic distinctions between the groups. It has been shown previously that lake whitefish probably survived the Wisconsin glaciation in both the Bering and Mississippi-Missouri glacial refugia. Recent geological evidence and the results of the present study regarding the distribution of populations of one of the groups favour isolation and dispersal from an additional refugium in the area of the present Nahanni National Park, N.W.T... Contact of the different refugial forms appears to have led to introgression in some cases but, in general, most populations remain genetically distinct even in the absence of physical barriers to gene flow.