THIS STUDY, COVERING BOTH TECHNICAL AND PUBLIC SERVICES, IS BASED ON TWO YEARS' OPERATION OF THE CENTRAL LIBRARY AND BRANCHES OF THE BALTIMORE COUNTY PUBLIC LIBRARY--THE LAST YEAR THE CARD CATALOG WAS USED AND THE FIRST YEAR OF USING THE COMPUTER-PRODUCED BOOK CATALOG. THE FIGURES, CONTAINING SOME EXTRAPOLATIONS, WERE OBTAINED FROM THE LIBRARY'S FISCAL-YEAR STATISTICS, SURVEYS, AND SAMPLING. SOME MAJOR CONCLUSIONS ABOUT THE BOOK CATALOG WERE THAT--(1) IT HAS BEEN AN ADDED EXPENSE, (2) MAINTENANCE COSTS SHOULD REMAIN STABLE OR DECREASE AFTER THE INITIAL EXPENSE OF ESTABLISHMENT, (3) THE MOST VALUABLE SERVICE ACCRETION HAS BEEN THE CATALOG'S UNION LIST FUNCTION FOR ALL LIBRARY AGENCIES, RESULTING IN GREATER USE OF THE COLLECTION AND A 51 PERCENT INCREASE IN INTERLIBRARY LOANS, (4) DISTRIBUTING THE CATALOG TO SCHOOLS AND ELSEWHERE IS USEFUL, (5) THE LACK OF BIBLIOGRAPHIC INFORMATION IN THE CATALOG IS OF SOME INCONVENIENCE FOR LIBRARIANS SERVING THE PUBLIC, (6) THE COMPUTER- PRODUCED BOOK CATALOG IS ADAPTABLE FOR USE IN A FUTURE INTEGRATED SYSTEM THAT WOULD INCLUDE OTHER LIBRARY FUNCTIONS, AND (7) COSTS CAN BE GREATLY REDUCED BY COOPERATING WITH OTHER LIBRARIES. APPENDED ARE SAMPLE BOOK CATALOG PAGES AND EARLIER ARTICLES ON THE BOOK CATALOG THAT APPEARED IN "WILSON LIBRARY BULLETING," NOVEMBER, 1965, AND "LIBRARY RESOURCES AND TECHNICAL SERVICES," SPRING, 1966. THIS STUDY WAS CONDUCTED UNDER A GRANT FROM THE COUNCIL FOR LIBRARY RESOURCES AND IS ALSO AVAILABLE FROM THE BALTIMORE COUNTY LIBRARY, 25 W. CHESAPEAKE AVENUE, TOWSON, MARYLAND 21204, FOR $1.00. (JB)