Sen. George Mitchell's 409-page report on performance-enhancing drugs in baseball describes a thriving underground market for steroids and human growth hormone. What began with just a few players and trainers expanded into a network of dozens, if not hundreds, of professional athletes. That network grew year by year as the players referred their friends and teammates.

Below, we present the findings of the Mitchell report as a social network. Players are connected to the person who first introduced them to the Mitchell report's star witness, Mets batboy turned personal trainer Kirk Radomski. In some cases, players met Radomski directly; in other cases they are several degrees apart. The statistical and visual analysis that went into making this chart was done using SocialAction, a software tool developed by Adam Perer and Ben Shneiderman at the University of Maryland's Human-Computer Interaction Lab. (Read detailed information on our methodology.)