A theoretical analysis of the method proposed by the AIEE committee on electrical machinery for measuring the negative-sequence reactance of synchronous machines is presented in this paper. The analysis proves that the method leads to a correct measurement of the negative-sequence reactance for the operating condition most frequently met in applying the method of symmetrical components, but that the method of measurement does not determine the correct negative-sequence reactance of the machine for the operating conditions used in the proposed AIEE test. The results of experimental tests are given to verify the theory presented.