The purpose of the present study was to assess the movement towards LSP testing and the usability of IELTS academic reading tests at the university level in Iran. The research question addressed was: Do learner variables such as levels of proficiency, background knowledge, and sex affect the performance of the participants on ESP reading comprehension tests? 245 university students, both male and female majoring in English literature, economics, medicine, electronics and chemical engineering from the universities ofIsfahan and Medical Sciences were selected to participate in the project. In three consecutive administrations, they were exposed to three different elicitation procedures: (a) locally constructed teacher-made EST reading tests, (b) a version ofIEL TS academic reading test, and (c) a version of the TOEFL test. The obtained data were, then, subjected to different statistical analyses (analysis of variance, two- and three-way ANOVA, and the post-hoc Scheffe tests). Filling these statistical procedures, three rather different results emerged: First, except for some minor cases, the gender of the participants was not related to the test performance. Second, levels of proficiency (high and low) affected the test performance of the participants on EST and IEL TS reading tests. Third, background, or (content area) knowledge did relate to the participants test performance on EST and IELTS reading tests, that is, the hypothesized interaction between students major fields of study and test content was confirmed. What can thus be implied from the results of the present research and their related interpretations is that language testers should take into account background knowledge when defining the construct of EAP reading comprehension tests. And to successfully perform on LSP tests, the subject area knowledge is surely regarded as a necessary factor ifnot a sufficient one. Finally, in this study IEL TS academic reading module, that was regarded as a distinguished example of the specific purpose proficiency testing, proved to be applicable at the university level in Iran.