Mutilating injuries of the hand and upper extremity result in tendon losses too great to be replaced by autologous grafts. The goal of this study was to use tissue engineering techniques to produce additional tendon material. We used a custom bioreactor to apply cyclic mechanical loading onto tissue-engineered tendon constructs to study ultimate tensile stress (UTS) and elastic modulus (E). Constructs used were acellularized rabbit hindpaw flexor digitorum profundus equivalents reseeded with tenocytes or left unseeded. Tendon constructs were subjected to a stretch force of 1.25 N over a 5-day course. Seeded tendon constructs that were exposed to bioreactor loading had a significantly increased UTS (71.17 +/- 14.15 N) compared to nonloaded controls (35.69 +/- 5.62 N) (p = 0.001). Similarly, seeded constructs exposed to bioreactor loading also had a significantly higher E (1091 +/- 169 MPa) compared to nonloaded controls (632 +/- 86 MPa) (p = 0.001). This study shows that cyclic loading of tendon constructs increases the UTS and elastic modulus of seeded constructs. The use of the bioreactor may therefore accelerate the in vitro production of strong, nonimmunogenic tendon material that can potentially be used clinically to reconstruct significant tendon losses.