Selective cannulation and injection of barium sulphate suspension into the arteries of isolated areas of peristeum of 21 vertebral bodies of cadavers aged 3 months to 51 years have been performed. This showed that in infants there is a very extensive intra-osseous arterial anastomotic network. Conversely, in normal adults the intra-osseous arteries were end arteries. The reduction in intra-osseous anastomoses probably had started by age 7 and had become almost complete by the age of 15 years. The blood supply of the adolescent and adult vertebral body is thus zoned into isolated regional compartments. These observations may help to explain the distribution of vertebral osteomyelitis, the possible aetiology of idiopathic adolescent scoliosis and the development of the 'step sign' in sickle-cell haemoglobinopathy.