Data was derived from a continuing research effort, the Drug Use Forecast (DUF). Interviews were conducted with recent arrestees within the Detroit Police Department detention facility covering both criminal and non-criminal behavior and an intensive drug use history. Each interviewee was asked to provide a urine sample for drug analysis. The data from the interview was correlated with the urinalysis result. Generally, it was found that the self-reported data of drug users is a reasonably reliable source of information. Substance type appears to be related to the probability of a non-concordant or invalid response. Cocaine users have a quite distinctly higher rate of nonvalid denial when compared to users of the other tested substances. The likelihood of non-concordant responses for cocaine users is around 4 to 5 times as great compared to marijuana or heroin use. While substance type appears to be related to degree of validity, intensity of use does not demonstrate any such relationship. Marijuana appears to have a distinctive distribution pattern within the non-concordant categories. It shows an inverted distribution of responses compared with both heroin and cocaine. 8 tables, 35 references.