The value of reciprocity in social exchange potentially comprises both instrumental value (the value of the actual benefits received from exchange) and communicative or symbolic value (the expressive and uncertainty reduction value conveyed by features of the act of reciprocity itself). While all forms of exchange provide instrumental value, we propose that the voluntary and uncertain nature of recurring reciprocal exchanges, in which actors individually give benefits to each other without formal agreements, make the act of reciprocity itself an important vehicle for conveying symbolic value. We experimentally test the value actors place on partners' voluntary acts of reciprocity--over and above the instrumental benefits obtained--by providing subjects with computer-simulated partners who systematically vary in the instrumental value, probability, and predictability of their reciprocity. Our results show that behavioral preferences are governed primarily by the instrumental value of exchange, while sentiments of trust, affective regard, and solidarity are strongly influenced by the symbolic value of constant reciprocity. We discuss implications for theories of social exchange and social capital. (Contains 3 tables, 2 figures, and 8 footnotes.)