Biomedical databases are an important source of information for health technology assessment. However, there is considerable variation in the costs of accessing commercial databases. We sought to measure the quality, amount of overlap, and costs of information retrieved from two of the main database sources--MEDLINE and EMBASE. Librarians at two health technology assessment agencies ran a total of eight literature searches on various medical technologies, using both databases. All search results were independently reviewed by two researchers. The researchers were asked to identify relevant references and to rank each of these according to a level of evidence scale. The results were tabulated to show the number of references identified by each database, the number of relevant references ranked by level of evidence, and the number of these references that were unique to one or the other database. The cost of retrieving references from each source was also calculated. Each database contained relevant references not available in the other. Because of the longer time lag for indexing in MEDLINE, many of the references that originally appeared to be unique to EMBASE were subsequently available in MEDLINE as well. Since our study was conducted, MEDLINE has been made available worldwide, free of charge, via the Internet. Hence, the cost difference between the databases is now even greater. However, notwithstanding the costs, it appears that literature searches that rely on only one or the other database will inevitably miss pertinent information.