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The minimum noise factor of a beam-type microwave amplifier is determined ultimately by the current and velocity fluctuations of the electrons in the beam, and may be conveniently expressed in terms of the noise parameters S and II. The paper describes a method of measuring these parameters by means of two cavities which couple to the noise fluctuations in the electron beam. The method has advantages over existing techniques in that it is flexible but not experimentally too complex. An analysis of the method is given in which the effects of thermal noise, and the finite bandwidth, of the cavities are taken into account.