It is often assumed that raw MT output requires post-editing if it is to be used for more than gisting purposes. However, we know little about how end users engage with raw machine translated text or postedited text, or how usable this text is, in particular if users have to follow instruc- tions and act on them. The research project described here measures the usability of raw machine translated text for Brazilian Portuguese as a target language and compares that with a post-edited version of the text. Two groups of 9 users each used either the raw MT or the post-edited version and carried out tasks using a PC-based security product. Usability was measured using an eye tracker and cognitive, temporal and pragmatic measures of usability, and satisfaction was measured using a post-task questionnaire. Results indicate that post-editing significantly increases the usability of machine translated text.