Abstract: OBJECTIVE: Evidence suggests that attentional threat avoidance is associated with increased risk for posttraumatic stress disorder (PTSD). This study evaluated the efficacy of two attention bias modification (ABM) protocols designed to enhance attention toward threats as a primary prevention of PTSD. METHODS: The efficacy of the two ABM protocols was assessed using a three-arm randomized controlled trial in 501 male combat-bound soldiers. One protocol used response-time (RT)-based ABM to train attention toward threat over neutral stimuli (dot-probe task); the other used an eye-tracking-based ABM employing instrumental reward to enhance sustained attention to threat over neutral stimuli. Each intervention was compared to a sham RT-based task (dot-probe) presenting only neutral stimuli. Participants underwent four sessions of active or sham training. Threat-related attention was measured before and after training. Self-reported symptoms of PTSD (primary outcome) and of depression and anxiety (secondary outcomes), were assessed at baseline and postcombat 1 year later. RESULTS: RT-based ABM delivered prior to combat exposure was associated with lower symptom severity and lower prevalence of probable PTSD postcombat relative to sham training (number needed to treat=22.7). A significant association was noted between training-induced threat attention and postcombat PTSD symptom severity in the RT-based ABM group. Eye-tracking-based ABM was not effective as a primary prevention protocol for PTSD symptoms. CONCLUSIONS: Consistent with a previous randomized controlled trial, RT-based ABM reduced risk for PTSD relative to sham ABM when implemented prior to combat exposure. These findings support the integration of RT-based ABM into resilience-building programs in military settings.