Self-diffusion coefficients of lead cryptates have been determined using a polarographic technique. The cryptands are sensible models of heavy and large particles undergoing Brownian motion. Self-diffusion coefficient measurements are in good agreement with mean spherical approximation transport calculations. Polarographic measurements show that the electroreduction of lead cryptate is an irreversible process. Hence, the standard rate constant k degrees of the couple Pb2+/(Pb)(Hg) can be deduced from the equilibrium constant of the complexation.