The aetiology of adolescent 5coliosis remains unknown and hindering research is the absence of an appropriate animal model. It is now well-established that pinealectomy in young chickens results in the development of scoliosis that has many of the characteristics seen in patients with adolescent idiopathic scoliosis but the mechanism underlying this phenomenon remains elusive. The principle product of the pineal gland is melatonin and so many studies have focused on studying the effects of reduced levels of this hormone. The results have been mixed and the role of melatonin remains un~ear. As melatonin production is inhibited by light, it was hypothesised that providing the chickens with an environment consisting of intense, continuous light would reduce serum melatonin levels and avoid any of the potential artifacts involved with the pinealectomy surgery. Consequently, pinealectomised and normal chickens were exposed to very intense light for complete 24 h in each day. At the end of 22 days in this environment serum melatonin levels had been reduced to very low levels in all chickens. Most importantly, 15% of the normal chickens had developed scoliosis and the number of pinealectomised chickens that developed scoliosis increased from 50% to 80%. The results showed that a method for reducing serum melatonin without pinealectomy has been established and which can be used in further experiments. Furthermore, the results also showed that reduced levels of serum melatonin has significant effects on the development of scoliosis. The indication is that there is a threshold level of serum melatonin below which scoliosis may develop probably in conjunction with some other factor which has yet to be identified.