This research tries to establish whether the Spanish public agenda during the period from 11 to 13 March, 2004, was set by the social media or the traditional media. Based on the content analysis of traditional media, such as CadenaSer, El Mundo and El País, and social media (mainly blogs and forums) it was concluded that the agenda of the social media, at a cognitive level, was actually established by the traditional media. It was also established that, during those three days, the social media worked as collectors of information from Spanish and foreign traditional media; as compilers of press releases from social organizations calling for demonstrations; and as diffusers of opinions linking the terrorist attack to the foreign policy of the Aznar Government, and of opinions that asked people to respond to terrorism through the polls. The agenda-setting, therefore, continued to be in the hands of the traditional media, not only at the basic level of the agenda-transfer of salience from the media to the public agenda-, but also at the attribute leveltransfer of the specific attributes-and framing of the terrorist attacks.