The lack of ethnic diversity in health research participation is a multi-dimensional problem. Racism and intersectional disadvantage compel us to use racial and ethnic categories to explore health, but race theorists warn that these can be essentialising and pathologising. Yet, the alternative, the pursuit of colour-blindness, can render the impact of race and ethnicity on health invisible. This paper describes the attempt to recruit an ethnically diverse sample to inform the development of an intervention for stroke patients. The study revealed deep uncertainties and tensions, which we use to re-examine our own positionalities and perspectives. We focus on the experiences of researchers and participants to show how 'usual' research practices are unwittingly exclusionary and promote 'methodological whiteness' (The British Journal of Sociology, 2017, 68, S214). Calls for greater diversity in research are frequently made, yet health research remains tainted by the use of problematic epistemological starting points, rendering participation by minoritised people uneasy. Medical sociologists, especially those engaged in clinical trials, have a vital role to play in recalibrating health research to attend to ethnicity and race. This requires us to reflect on our practices, to recognise where we are complicit in replicating social inequalities and to actively engage with communities to produce more inclusive research.