This study was conducted to learn the extent to which member institutions of the Association of Research Libraries (ARL) with Blackwell North America (B/NA) approval plans covering philosophy and political science are duplicating collections, and to determine what supplementary collection development practices are being used. Initial data were collected from 28 ARL member libraries that submitted profiles listing subject and non-subject parameters covering the subjects of philosophy and political science; additional data were collected by means of telephone interviews conducted with one or more respondents from each of the libraries and questionnaires completed by 25 of the libraries. It is concluded that the libraries studied use approval plans to a varying extent to meet the needs of their institutions' curriculum and to acquire core collections; that a variety of supplementary collection practices are being used; that size of collection and size of materials budget are apparently related to the breadth of variety reported; and that, although resource sharing is recognized as desirable in concept, it is not practiced extensively. Statistical data are presented in 10 tables and 1 bar chart; and appendices include the letter soliciting library profiles, the survey proposal and questionnaire, a telephone interview response sheet, and a listing of selections of the non-subject parameters reported by the libraries studied. (KM)