This report describes the methods used to monitor the loss of library materials at Purdue University's General Library during the last 20 years. Data are provided on the following: a complete facility inventory taken in 1959; spot checks of high loss areas made on the basis of patron requests; an availability study in which patrons revealed the types of problems users found in searching for materials; and a sample inventory taken with the aid of OCLC tapes. A bibliography lists seven references. (FM)