This paper examines how the drive to include minority ethnic groups in biomedical research raises challenging questions for the governance of some biobanks. Using findings from a qualitative study with researchers working at 10 UK biobanks that have been designed to explore common complex diseases, our study highlights the potential discordance between the twin imperatives of 'social inclusivity' and 'analytical acuity'. While the researchers interviewed were keen to include minority ethnic groups in their research, they were also concerned that this could have deleterious effects on the precision of their analyses. In our discussion of these findings we show that there remains considerable debate as to the impact of including participants from minority ethnic groups on analytical acuity. Nevertheless, a principle of justice requires that potential participants from all ethnic groups should be given the opportunity to participate in and benefit from biomedical research, and UK law requires public bodies (including research councils) to demonstrate that there is no unintentional or unjustifiable 'racial' discrimination in their activities. Researchers' concerns about analytical acuity could result in calls for study designs that examine every 'different' ethnic group, which would have consequences for the governance of some biobank studies and for efforts to challenge the discredited yet resilient idea that differences between ethnic groups are innate, essential and immutable. © 2008 A B Academic Publishers - Printed in Great Britain.