The biomechanical properties of human Achilles tendon are described with a computer-controlled material-testing machine. With an optimized fixation device for the muscle-tendon-calcaneus system the rupture was intratendineal. The tendons were compared for different rupture speed (1000 mm/min vs 100 mm/min), sex and age ( < 35 years vs > 35 years). The tendons ruptured at 1000 mm/min had better results in terms of maximum rupture force, stiffness and tensile stress, while the results for elongation and energy were less good. None of these differences were statistically significant. Significant differences were found between the sexes: male tendons had higher maximum rupture force and stiffness and a larger cross-sectional area. In the younger tendons significantly higher tensile rupture stress and lower stiffness were found.