Abuse of crack continues to be of major concern. Because of limits to biological testing, self-report has been the only mechanism for distinguishing crack use from powder use. Researchers have reported that smoking crack generates unique pyrolysis products that are detectable in urine, but no study has addressed how these products could be used as the marker for crack use, neither has any study addressed how reliable is the detection technology. The National Institute of Justice has developed a project to address these issues. The project consisted of (1) interviews conducted with and urine specimens collected from 2327 adult arrestees; (2) development and validation of procedures for routine GC/MS confirmation of crack use; and (3) establishment of standard profiles for two crack pyrolysis products, anhydroecgonine methylester (AEME) and ecgonidine (ECD). We found that AEME and ECD could be detected in urine specimens for periods of up to 40 hours. Most importantly, we demonstrated that to accurately measure crack use both AEME and ECD are necessary. Our results indicated that nearly 31% of the specimens were positive for undifferentiated cocaine, of which more than 88% were positive for crack. This resulted in crack prevalence rates of nearly 31% for females and 27% for males. These results will be used to further monitor the crack epidemic and to provide information that can inform the development of public policy as it relates to this drug.