The authors present an object-oriented approach to integrating organization and information system modeling. Characteristics and applications of object-oriented systems are first reviewed to show the evolution of the application of an object-oriented approach from an implementation and programming level to conceptual modeling of organization and information systems. The need to integrate organization and information systems is then discussed. MedaPlex, a metasystem implemented in Smalltalk language to support high-level object-oriented modeling is described in detail. Case studies defining critical success factors in MetaPlex and creating a structured electronic brainstorming system to support collaborative work are used to demonstrate the use of MetaPlex in integrating organization and information-system modeling at both individual and group levels.