During comprehension, a personal pronoun (he, she, it) refers to a preceding referent (boy, girl, child). This co-reference could be established, among other ways, by using (i) conceptual/semantic information (biological gender agreement between the pronoun and its referent), (ii) syntactic information (syntactic gender agreement), or (iii) both. This event-related brain potential (ERP) study assesses this interplay of syntactic and semantic information. We focussed on the N400 component, related to semantic integration, and the SPS/P600 component, related to syntactic reanalysis. The study was conducted in German, because its rich syntactic gender system offers a means to dissociate between biological (MALE/FEMALE) and syntactic gender (masculine/ feminine/ neuter), especially in the case of diminutives (das(neuter) Bubchen(MALE) [the little boy]). German subjects read sentences in which a referent (Bubchen(MALE-neutor)/Bub(MALE-masculine) [boy]) was introduced. Later a personal pronoun was presented which either agreed with the referent in terms of syntactic gender, or in terms of biological gender, or both, or violated both agreements. Overall, results showed salient P600 effects for pronouns. This indicates that the establishment of reference involves syntactic reanalysis. Furthermore, we observed N400 effects in sentences with non-diminutives, but not with diminutives. This shows that conceptual/semantic integration is involved during non-diminutive but not during diminutive pronoun processing, or at least it could not be violated. The overall pattern of results supports the claim that for non-diminutives, both syntactic and conceptual information is used to establish co-reference, while for diminutives the process might be purely syntactically driven.