In x-ray absorption spectroscopy, the accurate determination of the incident intensity (I0) has long been a difficult problem. Several techniques have been used to collect I0 data, but none have simultaneously obtained both I0 and I (transmitted intensity after absorption). The new technique described herein permits simultaneous determination of I0 and I utilizing a dual detector monitoring of the x-ray beam. With the sample removed, an intensity relationship between the two detectors, arranged in tandem, can be obtained. Knowing this relationship permits determination of I0 in the second detector during an experiment. The effects of voltage, current, and gas flow variations on this relationship are discussed, and an experiment is described where an absorption spectrum is obtained over an emission peak of the x-ray tube target material. The results of the experiment using two methods of obtaining I0 are compared.