Migration of I52Eu(III), 235Np(V), 237Pu(IV), 241Am(III), 99Tc(VII), and 99Tc(IV) was studied in natural fissures oriented parallel to the axis of granitic drill cores. A pulse of radionuclide solution was injected at one end of the fissure and the temporal change in radionuclide concentration of the effluent measured. At the end of each experiment the fissure was opened and the radionuclide distribution on the fissure surfaces measured. The radionuclide distribution ratios Ra, calculated from the measured retardation, correlate well to published distribution coefficients Kd. The increase in retardation of 235Np with increasing pH in the pH range 6 to 9 is in accordance with the hydrolytic equilibrium NpO2+ + OH‾ ⇄ NpO2(OH). Reduction of Tc(VII) to Tc(IV) resulted in a marked increase in retardation.