Joint brief of the United States, the Federal Trade Commission, and the Securities and Exchange Commission, as amicus curiae, addressing the application of the antitrust laws to activities subject to SEC regulation. The brief argues that collaborative underwriting activities occurring during the initial public offering of securities that are expressly or implicitly authorized under the securities laws, as well as conduct inextricably intertwined with such activities, are immune from the antitrust laws. It also cautions that antitrust claims in the securities context must be carefully scrutinized to ensure that legitimate underwriting activities are not chilled by vague or conclusory allegations of impermissible conduct. At the same time, the brief cautions that not all underwriting activities occurring in connection with an initial public offering enjoys a blanket antitrust exemption. The brief urges the Court to vacate the lower court rulings, neither of which struck the appropriate balance between the interests of both the antitrust and securities laws.