Undertaken to secure hard data on the nature and extent of American public library holdings of adult non-fiction books in the humanities, this study of 19 library collections of varying sizes used an inductive approach for evaluating books based on the frequency of their citation in selected reference tools. Five points summarize the findings: (1) 11 percent of the public libraries' total book holdings consists of adult non-fiction books in the humanities, or 15 percent of adult books and 22 percent of adult non-fiction held; (2) 50 percent of the titles analyzed were listed in three or more of the tools, 32 percent were found in one or two tools, and 16 percent were in none; (3) three-fourths of all the books noted were on literature and history, ranking as high or higher in quality than those in other subject areas; (4) libraries serving less than 25,000 persons compared well with those of other sizes; and (5) 70 percent of all titles held were published in the last 20 years. Tables detail the composition of the collections sampled and the distribution of their titles. (FM)