Prepositional phrase attachment was investigated in temporarily ambiguous sentences. Both attachment site (noun phrase or verb phrase) and argument status (argument or adjunct) were manipulated to test the hypothesis that arguments are processed differently than adjuncts. Contrary to this hypothesis, some previous research suggested that arguments and adjuncts are initially processed in the same manner, following a general bias to attach prepositional phrases to the verb phrase whenever possible [Clifton, Speer, & Abney (1991) Journal of Memory and Language, "30", 251-271]. The current study supports the hypothesis for differential processing, even during the initial stages of syntactic analysis. In an eye movement experiment, readers spent less first-pass time on argument prepositional phrases (PPs) than adjunct PPs. The results support a view in which a noun's or verb's argument structure can facilitate the analysis of its arguments.