A feature of contemporary Western, neo-liberal democracies is the frequent interaction between representatives of health and social services and the members of stigmatised and 'unruly' populations, such as injecting drug users. Previous research on drugs has tended to ignore the power relations and cultural dynamics at work in these encounters, and the ways in which they are framed by the wider neo-liberal context. Drawing on an ethnography of street-based heroin use in Melbourne, Australia's second largest city, I show how the discourses of both service providers and injecting drug users draw on wider neo-liberal values of independence, autonomy, rationality and responsibility. Service providers negotiate a framework of needs interpretation that creates and reproduces professional identities, and maintains boundaries between 'workers' and 'clients'. It also includes tensions around the definition of injecting drug users as 'chaotic' (i.e., failed neo-liberal) subjects, and slippage between service philosophies that emphasise a social model of health and forms of service delivery that emphasise the production of responsibilised subjects. For their part, street-based injectors construct an alternative framework of needs interpretation that emphasises their self-reliance, autonomy and independence, attributes and capacities largely denied them in service-provider discourse. In encounters with service providers, street-based injectors respond in various ways that include elements of resistance, strategic accommodation and the incorporation of therapeutic discourse. I conclude by considering the implications of my analysis for the future development of drug policy and practice.