We used psychophysiologic techniques to assess responses to imagery of psychologically stressful past experiences in medication-free Vietnam combat veterans classified, on the basis of DSM-III-R criteria into posttraumatic stress disorder (PTSD; n = 7) or non-PTSD anxiety disorder (anxious; n = 7) groups. Scripts describing each individual's combat experiences were recorded and played back in the laboratory. Ss were instructed to imagine the events the scripts portrayed while heart rate, skin conductance, and frontalis electromyogram were recorded. PTSD Ss' physiologic responses were higher than those of anxious Ss. A discriminant function derived from a previous study of PTSD and mentally healthy combat veterans identified 5 of the 7 current PTSD Ss as physiologic responders and all 7 of the anxious Ss as nonresponders. Results of this study replicate and extend results of the previous study and support the validity of PTSD as a separate diagnostic entity.