This paper aims to determine whether the apparent transitivity of the verb do in which + Noun Phrase (NP) + do, that + NP + do and this + NP + do constructions can be explained by the presence of a lexical do or if do is in fact an auxiliary. The electric corpora reveal that do is sometimes auxiliary in these structures (e.g. when it refers to a predicate denoting a purely stative event), sometimes lexical (e.g. when it is modified by an adjunct), but that the syntactic properties used as identification criteria for an auxiliary / lexical verb are not always iconic of the semantic-discursive criteria which appeared prototypical of each form of do in other structures. One upshot of the semantic unity between lexical and grammatical uses of do is the fuzziness of the category boundary between the lexical verb and the auxiliary. By contrasting two corpora, the British National Corpus and the Corpus of Contemporary American English, this study attempts to determine the lexical or grammatical nature of the verb do in prima facie borderline cases.