Stable isotope tracers offer a unique method to understand the fate and behaviour of trace metals in the environment.While there are many ways in which stable isotope tracers can enhance our ability to model and predict fate and behaviour,two aspects are of particular importance and present particular challenges; these are studies of the kinetics of uptake and loss and the determination of individual processes where there are simultaneous or competing processes involving the same metal.Particularly difficult is the determination of these processes in multi-compartment systems.This presentation will discuss the use of stable isotopes to investigate these two processes.Results from two studies will be presented to highlight both the potential and the challenges of using stable isotopes to untangle competing processes.Stable isotopes of Cd and Zn have been used to determine the relative differences in uptake and loss between the two metals in aquatic invertebrates.Data will be presented for two different species to illustrate the ability to separate simultaneous uptake and loss mechanisms.Similarly,stable isotopes of Hg have been used to separate uptake and loss in multiple organs of a mammal.Data will be presented that illustrate the unique ability of stable isotopes to determine the kinetics of movement among organs in the presence of a significant pool of background metal in the organs.