[en] Diffusivity measurement of cesium, strontium and sodiumlignosulfonate were made in a wet compacted clay. The density of the clay was 2.1 g/cm³ on an air dry basis. The temperature was 50 deg C. Strontium and cesium are ion exchanged into the clay and will thus be retarded. The measured diffusivities were 5.4.10^-11 m²/s for cesium and 3.3.10^-11 m²/s for strontium. These diffusivity values have been recomputed to describe a case with no ion exchange. In this way they are comparable with diffusivities of other small molecules. These are quite expected values and compare well with previous measurements with methane and hydrogen. Sodiumlignosulfonate with a mean molecular weight of 24000 could not be found on the recieving end of the diffusion cell after more than 800 hours. The diffusivity then must be less than 3.10 ¹⁴ m²/s