Chromium(III) is thought to be an essential element in mammals, its toxicity being very low. On the contrary, chromium (VI) is highly toxic to man, even if its effects are generally local, involving the respiratory tract and the skin. Once absorbed, chromium(VI) is quickly reduced to the trivalent form which accounts for all of this element present in the blood stream or taken up by tissues. As a result, any differences in systemic toxicity can only be attributed to differential solubilities and absorption rates. The kidney should be regarded as the critical organ, although tubular damage following occupational exposure is mostly due to acute absorption and transient in nature. Sensitive immunochemical techniques for the measurement of specific proteins in the urine have been used for the early detection of kidney damage, a possible threshold having been indicated at exposure levels yielding 15 micrograms/g creatinine in urine. Such a threshold has been confirmed by using monoclonal antibodies to reveal antigens from the brush-border of proximal tubules. Two main features of kidney damage were, however, apparent. The first one is the lack of dose-effect/response relationships, i.e. the lack of any progression toward more severe impairments when the exposure intensity increases. The second one is that the recent absorption rate more than the cumulated dose is responsible for the observed nephrotoxic effects.