The nephrotoxic responses of mammalian species, including humans, to injected, inhaled, ingested, and topically applied uranium compounds have been thoroughly investigated. Because there appears to be on unequivocal reports of uranium-induced radiation effects in humans, it is necessary to rely on experimental work with animals and on epidemiological investigations of human populations exposed to radium isotopes to infer human response to the alpha-particle emissions of uranium. Metabolic models have been developed to relate the intake of uranium in water and food to its uptake in the human skeleton and soft tissues. A US Environmental Protection Agency committee has recommended a limit for uranium in drinking water of 100 ug/L to limit effects on the kidney, which includes a substantial safety factor.