[en] Sorption properties and the migration of ¹²⁵I, ⁶⁰Co, ⁸⁵Sr and ¹³⁷Cs have been studied in Boda Claystone. The experiments were performed at ambient conditions using equilibrated groundwater and at in situ conditions with pore water under 100 bar. I was the most mobile element (D 10^-9 to 10^-11 m² s^-1). Cations migrate slower by one order of magnitude for Sr, and even more for Co and Cs. In order to extrapolate the data the retardation of isotopes relatively to the groundwater was estimated from sorption (Kd) data. Under diffusively controlled transport conditions the elements considered are able to migrate only a few hundred meters within a period of 10⁴ years from a repository. (author)