We describe a modular layered software architecture for automated laboratory instruments. The design consists of a sophisticated user interface, a machine controller and multiple individual hardware subsystems, each interacting through a client-server architecture built entirely on top of open Internet standards. In our implementation, the user-interface components are built as Java(TM) applets that are downloaded from a sewer integrated into the machine controller The user-interface client can thereby provide laboratory personnel with a familiar environment for experiment design through a standard World Wide Web browser: Data management and security are seamlessly integrated at the machine-conttroller layer using QNX(R), a real-time oper ating system. This layer also controls hard-wire subsystems through a second client-sewer interface. This architecture has pr-oven flexible and relatively easy to implement and allows users to operate laboratory automation instruments remotely through an Internet connection. The software architecture was implemented and demonstrated on the Acapella, an automated fluid-sample-processing system that is under development at the University of Washington.