Abstract: A method for testing tight cavities for leaks by a pressurization or depressurization technique (as herein defined), wherein a comparison is effected by means of a differential signal transmitter responsive to the difference between the pressure existing within the cavity and memorized supply pressure to the cavity, said comparison being effected by zero-setting the differential indication provided by the transmitter, independently of stabilization of the test cavity pressure, and taking the differential value of the two pressures as the initial datum or zero for verification of its increase with respect to time.