The paper describes S-VEX, the lexical acquisition component of the Swedish Core Language Engine (S-CLE). The S-CLE is a general purpose natural language processing system for Swedish developed from its English counter-part, the SRI Core Language Engine. In parallel with the development of the S-CLE, a Swedish version of the English VEX (Vocabulary EXpander) system was designed. S-VEX allows for the creation of lexicon entries by users with knowledge of an application domain but not of linguistics or of the detailed workings of the system. The approach taken is based on eliciting grammaticality judgments and information of inflected forms interactively from the user. The S-VEX system and the lexicon of the S-CLE is described, as well as the problems of the specific lexical acquisition task and their solutions.