None of the tests showed that the heroin shortage that began around Christmas 2000 increased the level of ATS consumption either contemporaneously or after a delay. Two possible reasons are offered for why these results differ from those obtained in interview studies of heroin users. First, it may be that the current study’s measures of heroin and amphetamine use, i.e., arrests for narcotic use/possession and amphetamine use/possession, are too weak or contaminated to detect a relationship between the trends measured; however, the fact that the study obtained consistent findings across independent measures suggests that the results are not just products of poor measurement. A second more likely possibility that explains the discrepancy between this study and interview studies is that some heroin users did move into the ATS market after the heroin shortage, but their contribution to the growth in ATS use was comparatively small. This report recommends further study on drug substitution in Australia. The current study involved two sets of analyses. The first involved an examination of the time series relationship between arrest for use/possession of narcotics and arrest for use/possession of amphetamines. The police arrest data were extracted from the Computerized Operational Policing System database over the period from January 1995 to September 2007 (the most recent data point available at the time of the study). The second part of the study involved a separate confirmatory analysis over a shorter time period, using quarterly data on emergency department admissions for heroin and amphetamines obtained from New South Wales Health. 10 tables, 3 figures, 6 notes, and 19 references