Synthetic biology provides a vivid and richly entangled contemporary example of a science being made public. A science, however, can be made public in different ways. A public could validate, legitimate, de-legimate, object to, verify, confirm or dissent from science. Practically, scientists could publicise sciencein the mass mediaor they could make science public. The contrast between high-profile, media scientists such as J. Craig Venter, and community-based participatory mechanisms such as OpenWetWare allows us to see how these alternatives play out in practice. While it is easy to criticise and dismiss the public-relations oriented promotion of synthetic biology by figures such as Venter, how should we evaluate the open participatory mechanisms of a social media effort such as OpenWetWare? I suggest, drawing on the work of Isabelle Stengers and Michael Warner, that the case of synthetic biology is interesting because many synthetic biologists commit themselves to making it public, and making its public-ness part of how it is done. They place hope in publics to make the science viable. At the same time, however, the publics who are welcomed into OpenWetWare are largely confined to validating the coordination mechanisms on which the claim to public-ness rests. Whether publics can do more than validate synthetic biology, then, remains a question both for publics outside and inside this emerging scientific field. And whether the alternatives of validation or participation themselves adequately frame what is at stake in the emergence of fields such as synthetic biology remains debatable.