Semantic feedback is an important source of information that a parser could use to deal with local ambiguities in syntax. However, it is difficult to devise a systematic communication mechanism for interactive syntax and semantics. In this article, I propose a variant of left-corner parsing to define the points at which syntax and semantics should interact, an account of grammatical relations and thematic roles to define the content of the communication, and a conflict resolution strategy based on independent preferences from syntax and semantics. The resulting interactive model has been implemented in a program called COMPERE and shown to account for a wide variety of psycholinguistic data on structural and lexical ambiguities.