A good lexicographical basis is needed for designing bilingual dictionaries that help users translate business texts. Many approaches have been suggested for including grammatical data in general dictionaries, but few have analysed the types of grammatical data relevant for bilingual specialised dictionaries. The theory of lexicographical functions is used to determine which grammatical data types are needed by specific user types. The analysis focuses on a bidirectional Spanish-English business dictionary, its treatment of prepositions in entries and cross-references to the middle matter texts. The findings show that the treatment is inconsistent and may mislead users, because their business-language competence is insufficient for producing correct translations. Bilingual dictionaries should offer a systematic treatment of prepositions and cross-reference users from entries to contrastive middle matter texts showing the specific uses of prepositions in business discourse. Finally, proposals on what to include and how this can be done are made.