A key limiting factor in the scale up and sustainability of HIV care and treatment programmes is the global shortage of trained health care workers. This paper discusses why it is important to move beyond conceptualising health care workers simply as 'inputs' in the delivery of HIV treatment and care, and to also consider their roles as partners and agents in the process of health care. It suggests a framework for thinking about their roles and responses in HIV care, considers the current evidence base, and concludes by identifying key areas for future research on health care workers' responses in HIV treatment and care in low and middle income settings.