Shells of the mollusc Cardium edule, collected from thirteen stations in Europe covering a wide range of temperature and salinity, have been analysed for strontium by X-ray fluorescence spectrometry. The inner shell layer is shown to have significantly higher Sr values than the outer layer, whose detailed analysis is the main concern of this study. There is an inverse relationship between Sr content and temperature but no evident relationship with salinity. The strong within- and between-sample variation does not appear to be controlled by variations in either growth rate or amount of shell secreted. Possible implications for palaeœcology are briefly discussed.