Sea water is observed to be a good desorbing agent for137Cs from marine sediments. Investigations on the sites of137Cs binding and their abundance by desorption over extended periods indicated that, whatever the time of contact of sorption,137Cs has three modes of desorption: fast component with desorption half-time of 30–50 min, medium component with desorption half-time of 25–50 h and slow component with desorption half-time of 31–112 days. These are expected to be sites of ion exchange, slower exchange and trapped Cs in the clay mineral layer lattices.