Injured tendons require mechanical tension for optimal healing, but it is unclear which genes are upregulated and responsible for this response. We unloaded one Achilles tendon in rats by Botox injections in the calf muscles. The tendon was then transected and left to heal. We studied mechanical properties of the tendon callus, as well as mRNA expression, and compared them too loaded controls. Tendon calluses were studied 3, 8, 14 and 21 days after transection. Intact tendons were studied similarly for comparison. Altogether 110 rats were used. The genes were chosen for proteins marking inflammation, growth, extracellular matrix and tendon specificity. In intact tendons, procollagen III and tenascin-C were more expressed in loaded than unloaded tendons, but none of the other genes was affected. In healing tendons, loading status had small effects on the selected genes. However, TNF, TGF-b1 and procollagens I and III were less expressed in loaded callus tissue day 3. At day 8, also procollagens I and III, LOX and scleraxis had a lower expression in loaded calluses. However, by day 14 and 21, procollagen I, COMP, tenascin-C, tenomodulin and scleraxis were all more expressed in loaded calluses. In healing tendons, the transverse area was larger in loaded samples, but material properties were unaffected, or even impaired. Thus, mechanical loading is important for growth of the callus, but not its mechanical quality. The main effect of loading during healing might thereby be sought among growth stimulators. In the late phase of healing, tendon-specific genes (scleraxis and tenomodulin) were upregulated with loading, and the healing tissue might to some extent represent a regenerate rather than a scar.