Carbon nanotubes (CNTs) are one of the first examples of nanotechnology, with a history of promising uses and high expectations. This paper uses the recent debate over their future to explore both ethical and value-laden statements which unsettle the notion of CNTs as a value-free nanotechnology and their regulation as purely a technical affair. A point of departure is made with the inclusion of CNTs on the Substitute-It-Now list by the Swedish NGO ChemSec, an assessment process that anticipates and complements (...) the Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) regulation in Europe. An argument map is constructed to illustrate the core contention in the debate—should CNTs be substituted or not—which follows from a systematic literature review and content analysis of sampled journal articles. Nine arguments are articulated that bolster one of two camps: the pro-substitution camp or the contra-substitution camp. Beneath these arguments are a set of three implicit values that animate these two camps in prescribing competing interventions to resolve the dispute: (i) environmental protection and human safety, (ii) good science, and (iii) technological progress. This leads to a discussion around the regulatory problem of safeguarding conflicting values in decision-making under sustained scientific uncertainty. Finally, the study suggests further empirical work on specific nanomaterials in a pivot away from the abstract, promissory nature of nanotechnology and other emerging technologies in science, technology, and innovation policy. The examination of ethics and values is useful for mapping controversies in science and technology studies of regulation, even amongst experts in cognate research fields like nanomedicine and nanotoxicology. (shrink)