An equation relating the potentiostatic current to the passage of time has been derived for the instantaneous nucleation and charge-transfer-controlled growth of two phases of a crystalline deposit under the restriction that both phases have the same density, molar mass, and ionic forms. The growth geometry of nuclei of each phase is represented by right-circular cones of a unique angle of contact. With the passage of time, the electrocrystallization process is shown to become increasingly dominated by the growth of the phase with the higher outward rate of crystal growth. Unlike the conical model of growth of a single-phase deposit which stipulates the attainment of a steady-state current plateau once the surface of an electrode is completely covered by the lateral growth of the deposit, in the two-phase electrocrystallization processes the attainment of the steady-state current is shown to be prolonged beyond the full coverage of the surface to a time when the phase with the smaller rate of outward growth is fully engulfed by the growth of the other phase. The transients due to the two-phase electrocrystallization reactions are shown to be indistinguishable from those of a single phase only if the rates of outward growth of both phases are set equal to each other. (C) 2003 The Electrochemical Society.