IMS was used to evaluate and assess exposure to a variety of illicit drugs among a group of persons with serious, self-admitted drug abuse histories. Its integration into and its use in an ongoing pretrial diversion program for nonviolent, first time drug abusing offenders was assessed. The pretrial diversion program consists of drug-abusing nonviolent offenders admitted for treatment and counseling in lieu of criminal prosecution. Abstinence from all mood-altering drugs is required during the program. Abstinence is monitored through regular use of drug testing, including the technology of radioimmunoassay of hair specimens for drug usage as well as urine screens based on conventional immunoassay technology. In this project, IMS has been added to this regimen. The IMS is a highly sensitive analytic chemical detector. The basic process includes the introduction of an unknown material, vaporization of this material by thermal energy, introduction of the vapor into a reaction or ionization region of the instrument, and release of the subsequent ionized material into a drift region or drift tube. The limitations to this technology include variable sensitivity to popular drugs to abuse depending on the suitability of the analyte material for ionization, and the appropriate cutoff values for routine operation of IMS are yet to be established. Of the 192 subjects in the study, 80.7 percent were assay positive at some point in their case history in diversion. The most frequently detected drug by IMS was cocaine; the most frequently detected drug by urinalysis was THC. Comparing the self-reported use of drugs to various assay outcomes showed that both radioimmunoassay of hair and general IMS revealed more cocaine use than was admitted to by subjects. It appears that persons in the diversion program are much more likely to be forthcoming about their marijuana use than about cocaine use. 8 tables, 7 figures, 4 references