A stereoradiographic technique is described in which two simultaneous x-ray exposures of an instrumented subject are prepared and analysed, yielding a complete six-parameter statement of the position and orientation of the instrument package relative to a coordinate system fixed in the subjects bony anatomy. A description of the radiologic equipment is included as well as details of those devices developed especially for stereoradiographic exposure and system calibration. The analytical aspects of the technique are discussed in qualitative terms in the body of the paper leaving more rigorous treatments to appendices. A statement of the inherent errors of this technique is also included.