Computer-based circulation systems, it is widely believed, can be utilized to provide data for library use studies. The study described in this report involves using such a data base to analyze aspects of library use and non-use and types of users. Another major objective of this research was the testing of machine-readable circulation data serving as the resource for a variety of computer-based studies. These studies were designed to supply information for decision-making in libraries in such areas as collection development and book budget allocations. This document reports upon a study of the value of computer-based circulation data in administrative decision making in a large academic library. Computer programs were written to produce a variety of outputs including listings for survey purposes of non-users/users; books most frequently used; use of the library by department or major of the user; and, the use of books by their classification code by academic level of user. It is the conclusion of this study that such experimental by-products of a computer-based circulation system offer useful data for book selection, budgetary allocation and the surveying of the library's clientele. A major question is raised as to what is library use/non-use. From the survey in this study it may be incorrect to categorize users or non-users as individuals who do or do not take out books for home use. (Author/SJ)