We present a simple but very secure non-compressive clampingdevice for in vitro tensile testingof the Achilles tendon in rats. Biomechanical studies were performed on 178 native and injured specimens without any registration of slippage out of the clamp. The average tensile strength of the native rat Achilles tendon was determined to be 48N (±11 N) and its displacement to failure averaged 0.8mm (±0.2 mm). The mean values for tensile strength within the injured tendons increased with time and were above the native tendon values from week 2 and later. Correspondingly, the displacement to failure decreased with time.