The Chemical Substances Information Network (CSIN) is a sophisticated switching network based on heterogeneous distributed data base management and networking concepts which were only theory less than a decade ago. CSIN offers efficient and effective access to on-line information resources (systems) containing data and information relevant to chemical substances, as well as information covering other scientific disciplines and subject matters. The purposes of CSIN are two-fold; first to meet the growing chemical data and information requirements of industry, academe, government (Federal and State), public interest groups, and others, and secondly to reduce the burden on the private and public sector communities when responding to complex Federal legislation oriented to chemical substances. CSIN is not another data base, but is a gateway system. CSIN links many independent and autonomous data and bibliographic computer systems oriented to chemical substances, establishing a 'library of systems.' Users may converse with any or all systems interfaced by CSIN without prior knowledge of or training on these independent systems, regardless of the hardware, software data, formats, or protocols of these information resources.