A high-precision method for determining the isotopic composition of cadmium (110Cd, 112Cd, 114Cd, 116Cd) has been developed and applied to study natural and anthropogenic materials such as sedimentary rocks, soils, corals and mining waste. Preliminary results obtained on sedimentary rocks, e.g. jurassic limestone, shale and greywacke, suggest the existence of natural variations in Cd isotopic ratios. The origin of this variation is likely to result mainly from a mass-dependent isotopic fractionation process. It is suggested that variation in the isotopic composition of Cd may also occur in materials of anthropogenic origin. Very low Cd concentrations (about 10 ppbw) are reported for the clastic rocks, whereas the limestone displays a much higher concentration (75 ppbw), suggesting that Cd may be trapped during diagenesis.