The radioactive isotope cesium-137 (₁₃₇Cs) is a recent addition to our environment, and due to its characteristically strong absorption by soil particles, it has become a valuable tool in the identification of modern sediments. The problems of the technique are illustrated by means of results from contrasting sites. In addition, the suggested ways in which the technique can be used in an archaeological context, despite the limitations, are discussed. See 20-147. -- AATA