Work sampling is an effective device for testing efficiency in the use of library materials and personnel. An administrator can determine whether circulation or reference librarians are effectively using their time and whether the work flow should be reorganized. Key operations of a sampling should include definition of a problem, identification of the pertinent categories, determination of appropriate observation times, mathematical processing of the data, and finally the interpretation. Statistical tables illustrate calculations of the study, and the figures illustrate tally forms. The appendixes contain additional mathematical refinements and a review of library literature on work sampling; and a 22-item bibliography includes books and articles on sampling. (Author/DS)