© 2018 Elsevier B.V. Relational values have recently emerged as a novel concept for research on human-environment relationships, seeking to understand ethical principles that may foster environmental stewardship, coupled with a recognition of nature's contributions to people. At present, most empirical research on relational values uses qualitative methods. Here we review some of the reasons that may have contributed to the lack of quantitative research, besides noting that a lot of existing quantitative empirical research on human-environment relationships already deals with relational values, even if it does not use that terminology. We suggest that incorporating quantitative approaches into the methodological toolkit of relational values research has a number of benefits: First, it contributes to the empirical evidence base testing hypotheses and assumptions emerging from qualitative and conceptual work. Second, it may help identifying core relational values shared across cultures, and this way improve communication and cooperation across different cultures. Third, it may improve the political legitimacy of environmental decision-making via statistically representative measurements of public views. Complementing qualitative with quantitative approaches for relational values research is also in the spirit of integrated valuation and value pluralism.