A general theory is developed, together with a simplified experimental procedure, which permits the absolute measurement of the magnitude and phase angle of any value of complex impedance, in terms of the characteristic impedance of a parallel‐wire line to which the impedance to be measured is connected as one termination. The observed quantities are the shape of the resonance curve of the current in one of the line's terminations obtained by varying the line length, and the length of line for maximum current. The effects of distributed line resistance and of radiation resistance on the impedance measurements are discussed in detail. Examples are given of the measurement of the impedance of straight resistance wires, and of the resistance of ``metallized'' resistors, at a frequency of 377 mc/sec.The accuracy of the method varies considerably throughout the total range of resistance and reactance, but is high for any combination of the two from a few ohms to a few thousand ohms. The possible accuracy varies approximately inversely as the frequency. At a frequency of 300 mc/sec. an optimum accuracy of about one percent may be expected.In an appendix some experimental data on the radiation resistance of a parallel‐wire line are described.