The NHS must increase productivity by 6% every year if it is to make projected efficiency savings of £21 billion by 2014. At the same time, it is expected to maintain or improve the quality of care. We know staff costs make up 60% of the NHS budget, so it is likely that both the number and composition of the 1.7 million-strong workforces will need to change in order to meet these targets. We argue that while substituting registered nurses with healthcare assistants (HCAs) is desirable in terms of financial benefits, there is not enough research evidence to identify the impact of changes or maximisation in skill mix upon efficiency (represented by the number of NHS cases treated) and the quality of care experienced by service users.