Students learning foreign languages often experience difficulty in mastering new vocabulary and expanding their lexicon. This paper attempts to clarify the role of the native language in the acquisition of new words. Does an adult learn foreign words quicker if the native language is employed (bilingual method) or if words are explained in the foreign language (monolingual method)? Some previous research indicates that use of bilingual wordlists yields better results than learning vocabulary in context or by a mixed method. For this experiment, groups of adult students in Sweden were taught new English words by monolingual and bilingual methods. Similar language lessons were taught each group, with the glossaries the only variables. Learning was tested with Test A, a variant of the cloze procedure. For Test B target-language questions based on texts read were asked, and questions were linked to definitions in monolingual glossaries. Results were consistently in favor of the bilingual treatment. (CHK)