As part of the Measurement Approaches to Partnership Success (MAPS) study, we investigated the relationship between benefits and costs of participation in long-standing community-based participatory research (CBPR) partnerships using social exchange theory as a theoretical framework. Three major findings were identified: (1) the concept of benefits and costs operating as a ratio, where individual benefits must outweigh costs for participation, applies to early stages of CBPR partnership formation; (2) as CBPR partnerships develop, the benefits and costs of participation include each other's needs and the needs of the group as a whole; and (3) there is a shift in the relationship of benefits and costs over time in long-standing CBPR partnerships, in which partners no longer think in terms of costs but rather investments that contribute to mutual benefits.