The self-diffusion coefficient of amphiphilic probes in the Lj phases of a surfactant system has been measured by fringe; pattern photobleaching (FRAPP) experiments. The variation of the diffusion coefficients with the surfactant volume fraction is in agreement with a model for diffusion in cubic phases, which allows to determine approximately the topology of the phases. The observed variation of the diffusion coefficients with the probe lengths agrees with the free-area model for surfactant diffusion.