Kump proposes: 1) to test a new approach (neutron activation) for distinguishing among the many stable isotopes of iron, and, 2) to find out whether enough fractionation occurs in nature to permit the use of iron isotopes to characterize the history of natural systems. The wide range of isotopic masses for iron (54 to 58), together with its involvement in microbially-mediated reactions, other redox reactions, diffusion, transport and precipitation, strongly suggest that isotopic effects are likely, and that their interpretation will lead to a better understanding of natural processes that are important both in research and in environmental assessment.