Given the occurrence frequency of any term within any set of articles within MEDLINE, we define -characteristic‖ terms as words and phrases that occur in that literature more frequently than expected by chance (at p < 0.001 or better). In this report, we studied how the cut-off criterion varied as a function of literature size and term frequency in MEDLINE as a whole, and have compared the distribution of characteristic terms within a number of journal-defined, affiliation-defined and random literatures. We also investigated how the characteristic terms were distributed among MEDLINE titles, abstracts, and last sentence of abstracts, including -regularized‖ terms that appear both in the title and abstract of the same paper for at least one paper in the literature. For a set of 10 disciplinary journals, the characteristic terms comprised 18% of the total terms on average. Characteristic terms are utilized in several of our web-based services (Anne O'Tate and Arrowsmith), and should be useful for a variety of other information-processing tasks designed to improve text mining in MEDLINE.