Thin sections of supragingival calculus from lower anterior teeth of 26 subjects were examined. From each specimen, an average of 10 spectra was collected from a densely-mineralized area less than 100 micron diameter. Only spectra showing peaks for minor elements or unusual Ca:P peak ratios were collected, stored and analysed semi-quantitatively. Ca:P weight percentage ratios varied within each specimen. Although most lay within the range 1.6 to 1.8, ratios of less than 1 and greater than 22 were obtained. The latter indicated the presence of some P-free Ca salts. The minor elements Mg and Zn occurred most frequently but the concentration within a specimen varied from the undetectable up to approx. 3 per cent by weight for Mg and 1 per cent for Zn. Low peaks for Ti, Ni, Co, As, Sr, Zr, Mo, Cd and Sn occurred in 1 to 3 spectra from a few specimens, indicating localized areas rich in one of these elements. Low to questionable Pb peaks were present in at least one spectrum from each of 20 specimens. There is thus a non-homogeneous distribution of Ca and P and of many minor elements throughout the calculus.