Research into the strategic impacts of information systems (IS) from the resource-based view of competitive advantage has increasingly embraced the indirect effect of IS on firm performance; that is, IS interact with other complementary organizational resources in influencing firm performance. Using both survey and archival data, this study set out to test the indirect effect of IS and determine the complementary organizational resources contributing to IS impacts on firm performance. The results provide additional evidence in support of the indirect performance effect of IS. Specifically, the study found that the performance impacts of IS arose from their interactions with firm-specific knowledge, information, vertical integration and related diversification that complemented IS.