This study aimed at investigating differential item functioning (DIF) on the Special English Test of the Iranian National University Entrance Exam (INUEE). The effect of gender and subject area was taken into account. The study utilized one-parameter IRT model with a sample of 36000 students who sat for the INUEE Special English Test in 2004 and/or 2005. The findings confirmed the presence of DIF on this test. The cloze test indicated the lowest DIF whereas language function indicated the highest DIF. The results also revealed some general gender DIF patterns across the subject area. Females were favored on the three sections of grammar, language function, and the cloze test, whereas males were favored on the vocabulary and word order sections. The reading comprehension section favored males and females equally. It was also concluded that the item format alone could not explain DIF. In other words, it is the subject area or the interaction of the subject area and item format that determines the degree and direction of DIF.
