Between September 2005 and April 2007, 350 fentanyl intoxication deaths were investigated and certified by the Cook County Medical Examiners Office. Investigations revealed that the majority of these fatalities were by intravenous injection of a white powder followed by a rapid collapse. The fentanyl was clandestinely produced in a lab in Toluca, Mexico and sold by the Mickey Cobra street gang. The term "Drop Dead" was coined for this "tainted heroin." Postmortem samples were screened by ELISA and confirmed by standard GC-MS methods. Fentanyl fatalities peaked at 47 per month in May and June 2006. Fifty-two percent were single fentanyl intoxications, with the remainder accompanied by either cocaine, morphine from heroin, or alcohol. This epidemic stressed the limited resources of the toxicology laboratory and autopsy service of the Medical Examiners Office. The clandestine lab was terminated, distributing gang members and leaders arrested, and the epidemic ceased in April 2007.