Designers of office information systems, which share various features with information systems and software development, need to carefully consider special issues such as document and communication flows, user roles, user interfaces, and available technology. The ESPRIT Project, Automatic TOols for Designing Office Information Systems (TODOS), proposes an integrated environment for office design with tools for requirements collection and analysis, conceptual design, rapid prototyping, and architecture selection. Conceptual design is a central phase of office system design: It provides correct and complete functional requirements from which the office prototype will be developed and the final architecture chosen. C-TODOS, the conceptual design support tool developed within TODOS, is presented in this paper. The purpose of C-TODOS is to give the designer tools for supporting conceptual modeling activities with the goal of obtaining correct, consistent, and good quality office-functional specifications. This paper presents C-TODOS within the TODOS development environment and describes the basic features of the tool: the TODOS Conceptual Model, the Specification Database, and the Modeling, Query and Consistency Checking Modules. The use of C-TODOS, through illustration of the development of a test case, and possible future research are discussed.