Subsequent to the 1977 lake restoration through whole-lake applications of alum (aluminum sulphate), Medical Lake, Washington, has supported an experimentally stocked rainbow trout (Salmo gairdneriRichardson) population. Because these fish and their prey are dependent upon habitat potentially higher in available aluminum than neighboring habitats, this study was undertaken to assess the possibility of aluminum bioaccumulation. Trout tissues, plankton and water were analyzed for total aluminum concentrations. Statistical comparisons of experimental and control tissues revealed few overall significant differences (P = 0.05) in the level of aluminum between alum-exposed and non-exposed fish, but significant differences existed between tissues within a given treatment and age class.