Steady-state voltammetry at microelectrodes and pulsed-field-gradient spin-echo NMR are compared as techniques for measurement of diffusion coefficients in solutions of polyelectrolytes. The NMR technique is well established in this application and thus is employed as a reference technique. We used Tl+ as a counterion probe, poly(styrenesulfonic acid) (PSSA) as polyelectrolyte, and LiClO4 as supporting electrolyte, to investigate the interactions of counterions with polyions in systems for various concentration. We measured Tl-205(+) Selfdiffusion coefficients by NMR and compared the NMR results with the results for gradient diffusion from voltammetry with microelectrodes. Identical results show that the electrochemical measurements are free of artifacts associated with the intrinsic interfacial nature of the experiment and confirm the identity of self- and gradient-diffusion coefficients under the range of conditions applied.