To determine which preconditioning and pretensioning techniques should be ap-plied to soft tissue grafts during anterior cruciate ligament (ACL) reconstruction to avoid loss of tension after surgery, fresh semitendinosus and tibialis anterior tendons underwent tensile mechanical testing with 4 pretensioning and/or preconditioning techniques. A mechanical tester was used to collect the data. Group I (n=5) was given only an initial 80 N pull for tensioning, Group II (n=4) was given pretensioning and initial tensioning, Group III (n=5) was given cyclic tensioning and initial tension-ing, and Group IV (n=5) was given a combination of the 3 techniques. Group I lost 50% of the initial tension at 30 minutes. The residual tension in Groups II, III, and IV was significantly higher than that in Group I after 1, 10, and 30 minutes (P<.001). Group IV consistently showed significantly higher residual tension than Groups II and III after 10 and 30 minutes (P<.05). All groups experienced elongation during testing: Group I (10.8 mm)<Group IV (14.6 mm)<Group III (15.6 mm)<Group II (16.6 mm), with significant differences observed between groups (P<.05). All experi-mental groups showed significantly greater stiffness than the control group (Group I) (P<.001). This study confirmed that pretensioning or preconditioning after 30 min-utes leaves a graft with higher residual tension. Moreover, pretensioning and precon-ditioning had an additive effect and resulted in significantly greater retained tension than either method performed individually. A simple pull up to 80 N before fixation does not impart sufficient tension to a graft to prevent it from failing. The authors recommend that clinicians performing ACL reconstructions with soft tissue grafts precondition or pretension the tendons before final tibial fixation to achieve greater retained tension in the graft after placement.