This thesis consisted of a series of studies that investigated how tendons respond to mechanical loading, and which factors lead to the production of matrix metalloproteinases (MMPs) by tendon cells. The working hypothesis was that MMPs are involved in the pathophysiology of tendon overuse injuries. An 11 week loading protocol did not induce an overuse injury in the rabbit Achilles tendon. A single loading bout of up to 6 hours duration did not lead to the production of MMP-1 and MMP-3 by the rabbit Achilles tendon, however injections of endotoxin or interleukin-l(3 (IL-1P) induced transient inflammation in the tendon, and the expression of these genes. Exposure of tendon cells to IL-1P or fluid-induced shear stress in vitro led to the expression and production of MMP-1 and MMP-3. Placing a rabbit Achilles tendon in organ culture was, in itself, a strong inductive stimulus for the expression and production of MMPs. In all, these results suggest that MMPs can be produced by a tendon if it is exposed to inflammatory cytokines, or its basal level of tension is reduced. The activity of these MMPs may damage the tendon matrix and lead to the manifestation of a tendon overuse injury.