The designation of the liquid-holdup on the base of the measurement of local film thicknesses is a special point of interest in connection with modelling hydrodynamics and heat and mass transfer of adiabatic and non-adiabatic separated two-phase flows. A new method of designation is performed by the application of the ultrasonic-recall princip. The local film thickness is calculated by the product of the sonic velocity in the liquid and the half of the run-time of the ultrasonic impuls in the liquid phase. Several reasons made the method to a useful instrument for experimentell studies: there is no contact between the sensor and the two-phase flow the calibration of the experimentell apparatus is unnecessary if the sonic velocity of the liquid is known very small values of film thickness are measurable statistic/stochastical description of the moved surface are possible the knowledge of special properties of the liquid phase are not necessary. Distributions of film thicknesses were measured under several flow conditions of the phases and several inclinations of the tube.