Glucosamine Sulphate is widely used by arthritic sufferers and athletes, with apparently no significant side effects. Nothing is known about the effects this compound has on active range of cervical spine motion. Rotation in the upper spine is important for accurate head positioning and may be related to the generation of headache. This study considers the effects of glucosamine supplementation on active range of cervical spine motion in asymptomatic human subjects.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 the study. Subjects gave their written informed consent. Cervical rotation was measured using a cervical range of motion device (CROM; Activator Instruments, USA). Measurements were taken in the afternoon. After the initial measurement, the subjects were given either glucosamine or placebo tablets and instructed how and when to take them. Measurements were repeated at weeks 2, 4 and 8 following the initial readings. 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 both placebo and glucosamine groups to have similar (p=0.98) total ranges of cervical rotation (placebo, 135 /-16 degrees: glucosamine, 135 /-15 degrees). During the experimental period, no adverse reactions were reported, however, four subjects either exited the study early or did not take the supplements as requested. Their data was not used in the final analysis. Over the 8-week supplementation period cervical rotation did not significantly change in the control group (placebo: final value 135 /-17 degrees). However, in the glucosamine group, there was a significant decrease (127 /-17 degrees; p=0.01). It would appear that glucosamine supplementation affects cervical rotation in asymptomatic human subjects. This might be a consequence of glucosamine deposition in vertebral joint structures.