Although social exchange theory has become one of the most oft-evoked theories in industrial and organizational psychology, there remains no consensus about how to measure its key mechanism: social exchange relationships (Blau, 1964). Drawing on Cropanzano and Byrne's (2000) review of contemporary social exchange theorizing, we examined the content validity of perceived support, exchange quality, affective commitment, trust, and psychological contract fulfillment as indicators of social exchange relationships. We used Hinkin and Tracey's (1999) quantitative approach to content validation, which asks participants to rate the correspondence between scale items and definitions of intended (and unintended) constructs. Our results revealed that some of the most frequently utilized indicators of social exchange relationships—perceived support and exchange quality—were significantly less content valid than rarely used options like affect-based trust. Our results also revealed that 2 direct measures—Bernerth, Armenakis, Feild, Giles, and Walker's (2007) scale and a scale created for this study—were content valid. We discuss the implications of these results for future applications of social exchange theory.