Human patellar tendon allografts are used to replace injured anterior cruciate ligaments. They are often stored by freeze-drying or freezing before use and have been sterilized by gamma irradiation or ethylene oxide gas. Studies comparing the mechanical properties of tendons preserved by freeze-drying and sterilized by ethylene oxide have yielded conflicting results. This study examined the effects of freeze-drying and ethyl ene oxide sterilization on the mechanical properties of human patellar tendons obtained from 11 human ca davers ; all were free of musculoskeletal disease. The 22 patellar tendons were halved longitudinally; 7 were fro zen at -70°C for 8 weeks and served as controls; 8 were freeze-dried; and 7 were freeze-dried and sterilized with ethylene oxide gas. Ultimate tensile stress and longi tudinal strain were greater for frozen than for freeze- dried, but not greater than freeze-dried, ethylene oxide- sterilized tendons (P < 0.05). The modulus of elasticity was similar in all tendon groups. The study suggests that some in vitro mechanical properties of frozen ten dons may be marginally superior to the properties of freeze-dried tendons, even after correction for size dif ference. Ethylene oxide gas sterilization had no adverse effect on tendon mechanical properties.