According to some theories of sentence processing, the human language processor relies mainly on syntax-based strategies when dealing with structural ambiguities. In this paper I show that the parser is also sensitive to the nature of the noun phrases' used and their discourse related properties. Dutch ‘which’ clauses are at least locally ambiguous between a subject–object and an object–subject reading. On the basis of syntax-based parsing strategies (e. g. the Active Filler Strategy, Frazier 1987), a subject–object preference is expected. However, several on-line and questionnaire studies show that the type of second NP affects the order preference: when the second NP is a non-pronominal NP the subject–object order is preferred, but more strongly so when the second NP is indefinite than when it is definite; when the second NP is a definite pronoun, in contrast, the object–subject order is preferred. A corpus study yields the same pattern, except for the non-pronominal definite NP cases: ‘which’ questions with a definite second NP more frequently occur in a object–subject rather than a subject–object order. This discrepancy can be explained in terms of the discourse status of the NP referent.