Exposure therapy treatment can lead to large reductions in posttraumatic stress disorder (PTSD) symptoms. Virtual reality exposure (VRE) therapy is designed to facilitate cognitive behavioral therapy for PTSD. During VRE therapy, patients go into an immersive computer-generated environment (go back to the scene of the traumatic event) to help them gain access to their memories of the traumatic event, change unhealthy thought patterns, gradually habituate to their anxiety, and reduce the intensity of associated emotions. The therapist's ability to manipulate the amount of anxiety experienced by the client during therapy is an important element of successful exposure therapy. Using a within-subjects design, 30 asymptomatic volunteers each experienced four levels of a virtual world depicting a terrorist bus bombing, designed to be increasingly distressful. There was a statistically significant difference between the mean subjective units of discomfort scores (SUDS) of the four levels, and several planned paired comparisons showed significantly higher SUDS ratings with higher simulation levels. Results suggest that sound may play an important role in successful elicitation of emotional responses during VRE. The results of this analog study provide initial validation of the potential of BusWorld to provide graded exposure for individuals suffering from PTSD originating from suicide bus bombings. Future research exploring whether VR exposure therapy with BusWorld can reduce PTSD in clinical patients is warranted.