The study adopts a genre analysis approach in order to investigate rhetorical variation in introductions of Arabic research articles from the fields of law and humanities. Fifty introductions from each discipline are analyzed in terms of the kinds of research justification and reader orientation they provide. The results show that law introductions exhibit more exponents of both functions; but neither discipline has utilized challenges to previous scholarship as a means of justifying the research proposed. These findings are accounted for through cultural, sociolinguistic, and educational factors that characterize the context of production of the texts considered.