A three-dimensional cervical spine range-of-motion system was developed using an electromagnetic tracking system for data collection and a personal computer for analysis and graphic representation of the data. A test was designed to investigate the sensitivity of the electromagnetic device to the proximity of metal. It was found that position errors could be kept below 0.5 cm, and rotation errors could be kept below 1.3°, if all metal was at least 33 cm from the source and sensor. The sensitivity of the system to metal should not cause serious problems in the typical clinical environment if simple precautions are taken.