The literature sources used in 461 consecutive problem-oriented questions submitted during 1993 to a Drug Information Centre were reviewed retrospectively. Journals were the most frequently used literature source (36% of all quotations). Commonly used medical and clinical pharmacology journals, together with standard textbooks, provided the necessary information to solve more than 50% of drug information requests. Most questions could be answered by including the complementary use of the question/answer database Drugline. Drug information access is important for the improvement of rational use of drugs. According to the present study, this activity is possible with a fairly limited number of sources.