There is a need for objective measurement of the carcass composition of sheep to apply to live animals (selection) and to the carcass itself (classification). Ultrasonic scanning of live sheep has generally produced disappointing results, and tissue depths measured by automatic probes on carcasses have not been as precise as the best visual scores for fatness. The application of the velocity of sound (VOS) technique to lamb carcasses in a previous study (Fisher and Page, 1986) measured composition at a hindlimb and neck site but was not as precise as fat scores in predicting lean proportion. A recent patent describes a method for determining the speed of ultrasound through soft tissues in the vicinity of bone (Miles, Fursey and Page, 1989), allowing measurements to be made across the back through M longissimus thoracis et lumborum and between the spinous processes of the vertebrae. This study uses that method to examine VOS measurements made at sites along the vertebral column in live sheep and carcasses.