Although the number of items borrowed through interlibrary loan may not increase as dramatically as it has in the past ten years, the trend can be expected to continue because of the growing interdisciplinary nature of biomedical research and because of the anticipated improved bibliographic control of biomedical literature. To provide a framework for collecting data on volume of flow between institutions, on time requirements for processing operations, on cost of interlibrary transactions, on the efficiency of communication channels, and on alternative procedures for performing the transaction, block diagrams were prepared to show the flow of information and materials between individuals and institutions. These diagrams show the interinstitutional dependence; any alterations in procedures in one institution affect other institutions. Even though it can be clearly shown where alterations in the flow pattern can be effected, there are little quantitative data available to serve as a justification for maintaining or modifying existing procedures.