Hospital health sciences libraries represent, for the vast majority of health professionals, the most accessible source for library information and services. Most health professionals do not have available the specialized services of a clinical medical librarian, and rely instead upon general information services for their case-related information needs. The ability of the hospital library to meet these needs and the impact of the information on quality patient care have not been previously examined. A study was conducted in eight hospitals in the Chicago area as a quality assurance project. A total of 176 physicians, nurses, and other health professionals requested information from their hospital libraries related to a current case or clinical situation. They then assessed the quality of information received, its cognitive value, its contribution to patient care, and its impact on case management. Nearly two-thirds of the respondents asserted that they would definitely or probably handle their cases differently as a result of the information provided by the library. Almost all rated the libraries' performance and response highly. An overview of the context and purpose of the study, its methods, selected results, limitations, and conclusions are presented here, as is a review of selected earlier research.