This research investigates the effect of the interplay of paralanguage and language on the accessibility of written texts. It identifies textual factors that may hinder the reader's understanding of the message. Studies of reading comprehension have traditionally concentrated on the language of texts. Many written texts, however, also rely on paralinguistic features to convey their messages, and to complement, illustrate, clarify and organise their content. Hence, it is paramount that a study investigating obstacles for reading comprehension be able to account for the complex web of paralinguistic devices present on the page. This work investigates such paralinguistic devices, focusing particularly upon the presentation of letters and words, the layout of the page, and the illustration of the written text. Parallel to the analysis of these nonlinguistic devices, language is also examined. A particular text type has been selected to provide the material for the analysis: emergency procedures. This choice was motivated not only by the fact that this text type is a rich source of paralinguistic and linguistic features, but also because accessibility in emergency texts is vital. In addition, emergency procedures are only minimally influenced by political, religious and other ideological factors. A corpus of 126 emergency procedures is analysed and related to the literature on paralinguistic features of written texts. Several combinations of linguistic and paralinguistic features are examined and, subsequently, hypotheses about how they affect the reading process are formulated. Verbal protocols and interviews are used to gain access to readers' interpretative processes when dealing with texts from the corpus. They aim to provide an insight into the reader's perception of the interaction of elements from both paralinguistic and linguistic structures and to evince accessibility problems. The application of this procedure both verifies the hypotheses and reveals new facts which were not predicted, thus increasing understanding of the factors which contribute to the accessibility of written texts