This document contains final and temporary regulations replacing the use of the Standard Industrial Classification (SIC) system with the North American Industry Classification System (NAICS) for determining what properties are of a like class for purposes of section 1031 of the Internal Revenue Code (Code). The text of these temporary regulations also serves as the text of the proposed regulations set forth in the notice of proposed rulemaking on this subject in the proposed rules section in this issue of the Federal Register. The final regulations consist of technical revisions to reflect the issuance of the temporary regulations.