Today, with various technology and business standards, organizations face rapid changes in both internal and external environments. To be able to rapidly respond to such changing environments, integration of software systems has entered among the top priorities of many organizations. However, despite extended use of software integration, methods for estimating the business value of implementing such integration are still missing. Besides presenting a conceptual model to define the benefits of systems integration and related causal relationships, this study proposes a method for measuring such benefits in monetary terms. In particular, we  demonstrate how a mathematical programming technique called Data Envelopment Analysis (DEA) can be used to evaluate the business value of software integration. Our method is illustrated using data from 12 organizations. The results indicate significant productivity gains by integrating software systems, which represent the value of software integration in organizations.