Adult lake whitefish (Coregonus clupeaformis) were fed As contaminated diets at nominal concentrations of 0, 1, 10 and 100 microg As/g food (d.w.) for 10, 30 and 64 days. Liver, kidney, stomach, intestine, pyloric caeca, gallbladder, skin and scales were analyzed for As content. The pattern of As accumulation in fish tissues was influenced by reduced feed consumption beginning on day 45 by fish fed the 100 microg As/g food. Significant As accumulation occurred in all tissues examined from fish exposed to the 100 microg As/g food for 30 days, with the exception of gallbladder. After 30 days of exposure, the highest concentration of As was observed in pyloric caeca of fish fed the 100 microg As/g food. Significant accumulation of As occurred in livers and scales of fish fed concentrations of As as low as 10 microg/g for 30 and 64 days. Muscle, gonad, spleen, gills and bone of lake whitefish fed a control diet for 10 days and 100 microg As/g food for 10, 30 and 64 days were also analyzed for As content. As concentrations increased in gonads, spleen and gills of fish fed the 100 microg As/g food for 30 days. Increased concentrations of As were observed in bone of fish fed the high dose food after each duration of exposure. As concentrations did not increase in muscle of fish after 10, 30 or 64 days of exposure. The following manuscript (Pedlar et al., 2001) documents toxicological effects observed in these fish. Analyses of As in pyloric caeca, intestine, liver and scales are recommended to evaluate the bioavailability of As to freshwater fish in environmental monitoring programs.