INTRODUCTION AND AIMS: Following detection of an upward trend in the frequency of fatal heroin overdoses in Victoria between 2001 and 2003, Victoria's Department of Human Services planned a campaign aimed at increasing injecting drug users' (IDU) awareness of overdose risks and prevention strategies. Stickers, wallet cards and posters featuring five key messages were distributed via needle and syringe programs (NSP) and other drug and alcohol services between November 2005 and April 2006. An evaluation of the campaign was commissioned to be conducted in late 2006. DESIGN AND METHODS: The evaluation consisted of analysis of three independent data sets--quantitative data collected from IDU during the campaign period (n = 855 at baseline; and a range of 146-656 at follow up); qualitative interviews with IDU who were NSP clients during the campaign period (n = 16) and qualitative interviews with NSP staff and other key stakeholders (n = 9). RESULTS: While key experts felt that the campaign messages had engendered lasting impact for at least some IDU, these positive impressions were not borne out by the NSP client data, with less than one quarter of all campaign messages being mentioned by a significantly higher proportion of clients during the post-campaign period compared with baseline. Key experts perceived the greatest weakness of the campaign to be the delay between issue identification and the introduction of campaign materials. DISCUSSION AND CONCLUSIONS: While IDU are generally responsive to health promotion campaigns, future initiatives in this domain should be designed and implemented rapidly and in ways that are sufficiently flexible to cope with shifts in drug markets which could influence the reception of key messages.