Glucosamine Sulphate is widely used by arthritic sufferers and athletes, with no significant side effects. Apart from biochemical activity, little is known about its actions on the biomechanical performance of the human body. This study considers the effects of glucosamine supplementation on active range of motion of the spine.A double blind placebo controlled trial was conducted on 38 subjects (aged 18-40yrs) who were randomly assigned into two groups, group A (placebo) and group B (1500mg glucosamine sulphate per day). Bro Taff medical ethics committee approval was obtained for this study. Subjects gave their written informed consent. The following measurements were made: total height (stadiometer, Cranlea UK), lumbar flexion (Schobers test), lower back and limb flexibility (sit and reach test), within 30 minutes of the subjects rising from bed and late in the afternoon. After the initial session, the subjects were given either the glucosamine or placebo tablets and instructed how and when to take them. Measurements were repeated at weeks 2, 4 and 8. Two examiners performed independent assessments on each subject at each occasion. Analysis used paired t-tests (SPSS), Data is represented as mean +/- 1 standard deviation. The initial data (n=38) showed a diurnal decrease in total height (a.m. 1.73+/-0.09m; p.m. 1.71+/-0.08m) along with an increase in both lumbar spine flexion (Schober test; a.m. 0.153+/-0.010m; p.m. 0.154+/-0.010m) and sit and reach (a.m. 0.49+/-0.13m; p.m. 0.52+0.10m). These values did not significantly change in the control (placebo) group over the 8 weeks. However, in the glucosamine group alone, there was a trend towards a decrease in lumbar flexion (both a.m. and p.m.; p=0.07), along with an increase in total height only in the morning (p<0.05).Therefore, glucosamine supplementation appears to affect human spinal range of motion.