Background Need‐altruism (a preference to help people in need) and kin‐altruism (a preference to help kin over non‐kin) underlie two hypotheses for voluntary blood donation: (i) Need‐altruism underlies motivations for volunteer blood donation and (ii) Black people express a stronger preference for kin‐altruism, which is a potential barrier to donation. This paper tests these hypotheses and explores how need‐ and kin‐altruism are associated with wider altruistic motivations, barriers, and strategies to encourage donation. Methods We assessed need‐ and kin‐altruism, other mechanisms‐of‐altruism (e.g., reluctant‐altruism), barriers, strategies to encourage donation, donor status, and willingness‐to‐donate across four groups based on ethnicity (Black; White), nationality (British; Nigerian), and country‐of‐residence: (i) Black‐British people (n = 395), and Black‐Nigerian people (ii) in the UK (n = 97) or (iii) across the rest of the world (n = 101), and (v) White‐British people in the UK (n = 452). We also sampled a Black‐Nigerian Expert group (n = 60). Results Need‐altruism was higher in donors and associated with willingness‐to‐donate in non‐donors. Levels of kin‐altruism did not differ between Black and White people, but need‐altruism was lower in Black‐British people. Kin‐altruism was associated with a preference for incentives, and need‐altruism with a preference for recognition (e.g., a thank you) as well as an increased willingness‐to‐donate for Black non‐donors. Need‐altruism underlies a blood‐donor‐cooperative‐phenotype. Conclusion Need‐altruism is central to blood donation, in particular recruitment. Lower need‐altruism may be a specific barrier for Black‐British people. Kin‐altruism is important for Black non‐donors. The blood donor cooperative phenotype deserves further consideration. Implications for blood services are discussed.