Taking as our starting point Parry and Greenhough’s (2018: 7) description of bioinformational data as ‘always relational’, we examine the long-term significance of kinship for how bioinformational data is generated and analysed, and how long-running cohort studies are maintained. We focus on the UK’s National Survey of Health and Development (NSHD), which tracks participants born in March 1946. Kinship, we suggest, is consequential for bioinformation, shaping both member participation and scientific analyses. Although dominant understandings of relatedness are significant, kinship exceeds such ideals: it entails complexity and difficulties. Archives, such as that of the NSHD, illuminate the open-endedness and situatedness of scientific practices and data, and register the vitality and vicissitudes of kinship.