Previous research has established that patients suffering from anxiety disorders, including post-traumatic stress disorder (PTSD), exhibit a cognitive bias that selectively favours the processing of threat material. This information processing bias has frequently been demonstrated by subjects' performance on the Stroop colour-naming task. The current experiment investigated the selective processing of threat information in people with PTSD using a modified Stroop procedure. Subjects were 13 ferry disaster survivors with high PTSD symptomatology, 20 survivors of the same disaster with low PTSD symptomatology, and 12 non-traumatized control subjects. All were asked to colour-name five types of words: ferry disaster words, general threat words, neutral semantically-unrelated words, neutral semantically-related words, and positive words. The disaster survivors with high levels of PTSD symptomatology evidenced a significantly longer response latency for colour-naming disaster-related words than for other word types. The results of the low-PTSD survivors and non-traumatized controls showed no significant difference between response latencies for general threat words and disaster word, although all 3 groups showed increased latencies for threat words compared with neutral words. The mechanisms proposed to underlie this response pattern are discussed, and clinical implications are considered.