Glucosamine Sulphate is widely used by athletes and sufferers of osteoarthritis (OA). Little is known about the actions of this supplement on the biomechanical performance of the human body. This study considers the effects of glucosamine on active spinal range of motion in healthy subjects. A double blind placebo controlled trial was conducted on 38 subjects (aged 18-40yrs; written informed consent obtained) who were randomly assigned into two groups: group A (matched placebo tablets), group B (1500mg glucosamine sulphate per day). The following measurements were made within 30 minutes of the subjects rising from bed and later in the afternoon: lumbar flexion (Schober test), lower back and limb flexibility (sit and reach test). Cervical rotation was measured in the afternoon only, using a cervical range of motion device (CROM; Activator Instruments, USA). After the initial afternoon assessment, the subjects were given 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 presented as mean+/-1SD; Coefficient of variance. 5 subjects failed to complete the experiment: n=18 (group A) and 15 (group B). A diurnal increase in both lumbar spine flexion (Schober test) and sit and reach capability was found throughout. No change was found in the control (placebo) group from week 1 to week 8, however, there was a trend towards a decrease in lumbar flexion (both a.m. and p.m.; Table 1) in the glucosamine group. In both the Schober test and cervical rotation, the overall change reported for the glucosamine group was seen in a large proportion of the subjects in that group; 10/15 and 13/15 subjects, respectively. Although the differences appear small, both measures of spinal flexibility showed change in the same direction, whereas the sit and reach test (mainly hamstring flexibility) showed no change. A decreased spinal flexibility might increase stability and reduce predisposition towards injury in this age group (i.e., athletes). However, further study is required to determine the presence and significance of these potential changes in both athletes and those with OA.