A distributed multiparty desktop conferencing system called MERMAID, is described. This system allows a group of users, seated at their desks, to conduct a meeting from their personal computers (PC). Participants can jointly view and process multimedia conference documents, including text, graphics, scanned images and handwritten figures they are sharing, and they can simultaneously interchange voice and video images through ISDN, IVD-LAN(Integrated Voice and Data LAN which has a common line interface of both ISDN and Ethernet) , satellite network and high speed data network. The MERMAID is implemented by using OS/2 based PCs with electronic writing pads, image scanners, microphone-installed loudspeakers, video cameras, etc. The MERMAID[Sakata90; Watabe90] is designed based on Group Communication Architecture (GCA). GCA is a framework for supporting group cooperative work in a distributed environment. It consists of two models: a function model, which defines hierarchically structured service functions, and a system model, which provides client-server model based service interfaces and multimedia communication protocols. MERMAID has been proven effective and feasible through daily use evaluation by around thirty members, involved in such activities as collaborative software design and development among distributed offices and laboratories.