A fast method has been developed to determine the position of the outlines of bony structures on X-ray photographs of the cervical spine movements in the sagittal plane (105 mm spot film camera; 4 frames per second; about 10 seconds per complete anteflexion-retroflexion or vice versa). This method corrects for incongruity of the vertebral contours on consecutive frames due to motion in another than the sagittal plane. It also automatically corrects erroneously marked points. This method has been used to determine segmental range of motion (SROM) and total range of motion of the head with respect to the seventh cervical vertebra (TROM). It is shown that SROM may be larger when frames of intermediate instead of extreme positions of the film are considered. In ten test persons without cervical complaints the interindividual variability of SROM turned out to be comparable to the ones found with older methods. Intraindividual variability of SROM and TROM was determined by registration at three different measuring sessions (0, 2 and 10 weeks). This intraindividual variability is high, especially in the cranial and caudal parts of the cervical spine. It is concluded that SROM and TROM are unsuitable to be used as a parameter of cervical spine mobility.