abstract: the present study is an attempt to find out cultural exophoric references in iranian high-school elt textbooks and touch stone series to compare the frequency of occurrence of such references in these books. the purpose is to find out which of the series of the books under investigation impose a greater referential burden on efl learners as far as their reading comprehension of the text is concerned. the researcher extracted all the cultural exophoric references used in these coursebooks by reviewing the texts sentence by sentence to locate any references used in the texts exophorically. to this aim, the number of exophoric references which were used in ten thousand words of each text was computed. moreover, in order to see which of the two series impose a greater referential burden on efl learners, the cultural exophoric references extracted from the series were categorized according to their type; that is, whether they refer to people, places, natural resorts, cultural/historical heritage, and whether they are comprehensible to learners or require reference sources or authorities for them to understand the references. as the findings show, touch stone series made greater use of cultural exophoric references in comparison with english book series. moreover, touch stone 2 and english book 1 used more cultural exophoric references in comparison with the other three coursebooks of each series. furthermore, in terms of reference to people , natural resorts and cultural/historical heritage, touch stone series, and, with regard to reference to places, english book series imposed a greater referential burden on efl learners. considering comprehensibility, the greater number of cultural exophoric references in touch stone series made these textbooks more difficult for efl learners to comprehend them and required reference sources or authorities for them to grasp their content. key words: cultural exophoric reference; referential burden; high-school elt textbooks; touch stone series;cohesion. supervisors’ signature