This contract is for the purpose of obtaining the following Chemical Abstracts Service (CAS) information products: (1) CAS Registry Services, (2) CHEMLINE Support, and (3) Special Studies and Programming Efforts. (1) CAS Registry Services: NLM submits to CAS the files of substance data which have been obtained from a number of sources. The major source comes from new chemicals indexed for the MEDLINE database, MESH chemical records for which there are no CAS Registry Numbers are submitted to CAS for name match and then chemist review in order to add this data to MESH and MEDLINE. NLM also supports the addition of CAS Registry Numbers to other files such as the Registry of Toxic Effects of Chemical Substances (RTECS), which is available online in the TOXNET system. (2) CHEMLINE Support: CAS maintains the CHEMLINE profile and keeps it up to date by the addition of and/or deletion of substance records as they are identified by NLM for incorporation into the file, or identified by CAS as being inaccurate. The registration process for CHEMLINE is similar to the service described above, but goes further by helping NLM to main maintain CHEMLINE as an accurate and up-to-date file. (3) Special Studies and Programming Efforts: As changes to the CHEMLINE Maintenance System or other services to NLM become necessary, CAS provides systems analysis and programming for necessary modifications to these programs.