This paper explores the role of semantic transparency in the representation and processing of English compounds. We focus on the question of whether semantic transparency is best viewed as a property of the entire multimorphemic string or as a property of constituent morphemes. Accordingly, we investigated the processing of English compound nouns that were categorized in terms of the semantic transparency of each of their constituents. Fully transparent such as bedroom are those in which the meanings of each of the constituents are transparently represented in the meaning of the compound as a whole. These compounds were contrasted with compounds such as strawberry, in which only the second constituent is semantically transparent, jailbird, in which only the first constituent is transparent, and hogwash, in which neither constituent is semantically transparent. We propose that significant insights can be achieved through such analysis of the transparency of individual morphemes. The two experiments that we report present evidence that both semantically transparent compounds and semantically opaque compounds show morphological constituency. The semantic transparency of the morphological head (the second constituent in a morphologically right-headed language such as English) was found to play a significant role in overall lexical decision latencies, in patterns of decomposition, and in the effects of stimulus repetition within the experiment.