E.H.D. impedance technique was used to investigate two typical electrocrystallization cases where the current is, at least partially, limited by mass transport. In the case of Te electrodeposition, it is shown that the E.H.D. responses of microdendritic layers are similar to that of a flat partially blocked surface, and allow an in situ evaluation of a characteristic size d of the dendritic structure. The transition between smooth and dendritic layers as well as the variations of d vs various parameters were investigated in order to illustrate the possibilities of the method. In the case of CdTe electrodeposition, E.H.D. impedances indicate that a slow surface process is involved in the definite compound formation. The surface concentration of cations differing from zero, the deposits are smooth and compact.