The aim of this study was to examine changes in drug use patterns among groups of injecting drug users (IDU) who remained in the drug market during a period of reduced heroin availability in NSW, Australia. Cross-sectional data collected from regular IDU interviewed as part of the NSW Illicit Drug Reporting System (IDRS) between 1996-2003 were analysed. Drug use patterns, reported drug availability and price were assessed. There was a marked decrease in the frequency of heroin use during the period of reduced availability in 2001, with some increase in 2002 and 2003. Heroin availability and frequency of use have not returned to levels reported prior to 2001; however; even at the peak of the reduction in supply, users continued to access heroin. There was a significant shift among IDU from heroin to cocaine during 2001, which subsequently reversed. The availability of cocaine has fluctuated in recent years, but the price has remained stable. The price of heroin appeared to be more responsive to market fluctuations, and co-varied with heroin availability. IDU used cocaine when heroin was less available; however, patterns of cocaine use were not maintained. The frequency of heroin use remained lower, which may be indicative of a less consistent supply, increased price or increased numbers of IDU entering treatment. The reduced supply of heroin in 2001 highlighted the adaptable nature of IDU patterns of use, indicative of the need for a commensurate treatment response. It also highlighted the importance of the ongoing monitoring of drug trends in Australia.