Pursuant to a legislative requirement, GAO reviewed the Securities and Exchange Commission's (SEC) new rule on the regulation of exchanges and alternative trading systems (ATS). GAO noted that: (1) the rule would allow ATS to choose whether to register as national securities exchanges, or to register as broker-dealers, depending on their activities and trading volume; (2) in addition, Regulation ATS will require alternative trading systems that trade a certain volume of securities to make their best prices known to the public and allow non-subscribers access to those prices; (3) the final rule would also amend Rules 6a-1, 6a-2, and 6a-3 regarding registration as a national securities exchange; and (4) SEC complied with applicable requirements in promulgating the rule.