Psychologists increasingly recognize the importance of relational responding in understanding human behavior. As a result, there is the growing need for good measures of relational responding. One promising measure is the Relational Abilities Index (RAI). However, its measurement properties have not been explored in-depth. There is little understanding, for example, of how precise the RAI is as a measure of individual-level abilities. In this paper I examine this and other measurement properties of the RAI and assess its suitability as a measure of relational responding at both the individual- and group-level. Although broadly promising, the measure exhibits several substantial shortcomings which limit its utility and interpretability. I make recommendations for how to improve the measure and highlight the importance of in-depth examinations of measurement for future research.