A linear analysis of the stability of the flow in a laminar boundary layer under conditions of intensive interphase mass transfer between two liquids, when high mass fluxes through the phase boundary induce secondary flows, is suggested. The first liquid is in motion over the second one (in rest). Hydrodynamic stability in the two phases is considered. The critical Reynolds numbers in the first place are obtained at different intensities of non-linear mass transfer in the laminar boundary layer. The influence of the direction of the intensive interphase mass transfer on the hydrodynamic stability is analogous to the cases where phase boundary is motionless, but depends on the distribution of the diffusive resistance in the two phases. The motion of the interface is considerably more intensive than the one in the gas-liquid system, which leads to an increase in the stability of the flow to a large degree. The flow is stable at a large Reynolds number in the second phase.