Vietnam combat veterans with current posttraumatic stress disorder (PTSD), with other Axis-I disorders, or with no Axis-I disorders completed a series of tasks designed to elucidate the psychophysiological parameters of information-processing in PTSD. These tasks included a modified Stroop procedure (MSP), a standard Stroop procedure, a recognition memory task, and a threat rating task. Physiological responses were recorded throughout the study. Our data supported several predictions derived from information-processing models of PTSD. PTSD subjects exhibited greater MSP interference to high threat words than both comparison groups, and a liberal response bias toward recognizing military-related words. PTSD symptoms and threat reactions contributed to MSP interference effects for high-threat words after controlling for medications, depression, and baseline physiological activity.