Tendon tissue and the extracellular matrix of skeletal muscle respond to mechanical loading by increased collagen expression and synthesis. This response is likely a secondary effect of a mechanically induced expression of growth factors, including transforming growth factor--1 (TGF--1) and insulin like growth factor-I (IGF-I). It is not known whether unloading of tendon tissue can reduce the expression of collagen and collagen-inducing growth factors. Furthermore, the coordinated response of tendon and muscle tissue to disuse, followed by reloading, is unclear. Female Sprague-Dawley rats were subjected to hindlimb suspension (HS) for 7- or 14 days, followed by 2-, 4-, 8- or 16 days of reload (RL) (n=8 in each group). Age matched controls were included for day 0, day 14 HS and day 16 RL (n=8). mRNA expression levels for collagen I (COL1A1), collagen III (COL3A1), TGF--1, connective tissue growth factor (CTGF), myostatin and IGF-I isoforms were measured by Real-Time RT PCR in soleus tendon and -muscle. The tendon mass was unchanged, while the muscle mass was reduced by 50 % after HS (p<0.05) and returned to control levels during RL. Collagen I and III, TGF--1 and CTGF mRNA levels were unaltered by HS, though collagen III tended to decrease in muscle at day 7 HS. IGF-I isoforms were significantly induced in tendon after 7 days of HS (p<0.001) and MGF increased in muscle at day 14 HS (p<0.05). Reload increased muscle collagen I and III mRNA (> 10-fold) (p<0.001), and growth factor expression (p<0.05), while the tendon response was limited to a moderate induction of collagen expression (2-fold) (p<0.05). Unloading of tendon and muscle tissue did not reduce expression of collagen and collagen-inducing growth factors, indicating that the response to unloading is not opposite that of loading. Furthermore, the tendon response was clearly different and less pronounced than the muscle tissue response.