For reporting year 2003, Los Alamos National Laboratory (LANL or the Laboratory) submitted Form R reports for lead, mercury, and nitric acid as required under the Emergency Planning and Community Right-to-Know Act (EPCRA), Section 313. No other EPCRA Section 313 chemicals were used in 2003 above the reportable thresholds. This document was prepared to provide a description of the evaluation of EPCRA Section 313 chemical use and threshold determinations for LANL for calendar year 2003, as well as provide background information about data included on the Form R reports. Section 313 of EPCRA specifically requires facilities to submit a Toxic Chemical Release Inventory Report (Form R) to the U.S. Environmental Protection Agency (EPA) and state agencies if the owners and operators manufacture, process, or otherwise use any of the listed toxic chemicals above listed threshold quantities. EPA compiles this data in the Toxic Release Inventory database. Form R reports for each chemical over threshold quantities must be submitted on or before July 1 each year and must cover activities that occurred at the facility during the previous year.