This paper explores the comparative and cumulative influence of a number of factors on the perceived level of cooperation in a dyadic relationship. Drawing upon the transaction costs economics, organization theory and information systems literatures, we hypothese three sets of key influences: (1) factors exogenous to the relationship, i.e., the characteristics of the environment within which the relationship operates, and factors endogeneous to the relationship including (2) economic and behavioral characteristics of the relationship, and (3) interorganizational information technology applications. These factors have been independently examined in separate research streams. A key contribution of this study is therefore to conceptually and empirically capture their collective influence on cooperation. We empirically test the five hypotheses we develop within the context of buyer-supplier relationships in the U.S. and Japanese automobile industries. Multiple regressions conducted on a data set of 447 distinct relationships indicate that the relational characteristics (i.e., the behavioral climate of the relationship) are the most robust predictor of cooperation in both countries when compared with other structural (e.g., asset specificity) or technological factors (use of EDI--electronic data interchange). Environmental uncertainty (i.e., technological unpredictability) is positively associated with cooperation in Japanese supplier relations, which suggests that cooperation can act as an uncertainty absorption mechanism. Governance structure is a strong and significant predictor of cooperation in both samples, but with the opposite sign. Similarly, information technology (IT) does not play the same predictive role in the two country samples. Significant only in Japan it reflects an 'electronic partnership' approach to the use of IT in supplier relations.