Over the last decade, studies of online catalogs have revealed that they frequently discourage users. Subject queries often fail to produce retrievals or produce retrieval sets that are too large and unwieldy to be easily scanned. Research shows that users are seeking alternative approaches to those that manipulate the subject headings in catalog records. This document reports on the development and evaluation of the ASTUTE experimental online catalog, which makes use of search trees to enhance subject access. The project investigated whether search trees actually improved the search performance of subject searchers at the terminal and whether users liked the concept of controlled system responses; they also were designed to assemble a list of characteristics of the types of queries that ASTUTE failed to answer. Chapter 1 describes circumstances and factors that gave rise to the ASTUTE project. Chapter 2 reviews previous research on subject queries and search trees. Chapters 3, 4, and 5 describe the development of the experimental catalog. Chapter 6 discusses transaction logs and related methodologies that were used in testing the system's retrieval. Chapters 7 through 12 present analysis of the online retrieval test data, including user behavior, precision and recall, and failure analysis. They also explore resulting ideas for redesigning the search trees. Chapter 13 is a summary of project activities, findings, and recommendations. Some specifics on search trees, sample questionnaires and consent forms, and transaction log records are appended. (Contains 99 tables and 113 figures.) (BEW)