The spinal movements in maximum arching, dipping and left and right lateral flexion were measured in 10 horses without signs of back pain. A system for motion analysis (Expert Vision System) was used to identify the position of the markers placed on the head, the spinous processes of T5, T10, T16, L3, and on 2 of the sacral spines, By definition, the maximum of the spinal movement was set when the T16 marker reached its maximum deviation from the start position. The difference between start position and maximum position was presented as per cent of the horse's height at the withers. At T16 the mean results for flexion (arching) of the back were 5.9% (s.d. 0.9), for extension (dipping) -2.4% (s.d. 0.7), for flexion to the left 4.2% (s.d. 1.1), and for flexion to the right 5.3% (s.d. 1.3).