From the inception of the first Index Medicus, published in 1879, to the present, the National Library of Medicine has been concerned with the quality of journals in the Index. The Library has, therefore, sought advice repeatedly on how best to maintain currency of the Index without sacrificing quality and subject matter balance. Responding to suggestions, the Library decided in June 1964 to base its selection of journals on recommendations made by a panel consisting primarily of extramural consultants widely regarded as specialists in the totality of biomedical literature. Beginning with its first meeting in September 1964, this panel has been fortified in its reviews by advice from subject matter specialists. The panel, by its own wishes, which bear the endorsement of the Board of Regents of the Library, will continue to rely heavily on such expert advice in future evaluations of journals.