Two crucial steps in the design of the user interface for an ISDN application are discussed. In the first study, a passive prototype, in which pictures of application screens were shown to subjects, allowed users to state their expectations about the system in the absence of bias owing to system feedback. Subjects interpreted graphical elements of the application window, described their expectations about multistep procedures (call conference, call transfer, and database access), and learned to operate a proposed user interface. In the second study, the user expectations for multistep procedures obtained in the first study were used as blueprints for constructing two syntaxes for system operations. These alternative syntaxes, along with the syntax contained in the design proposal, were then prototyped and evaluated using the Supertalk language. The prototype program provided system responses according to one of three syntaxes, played voice files to simulate calling/called party actions, and collected data. An experiment was conducted to estimate effects due to syntax type and task type.>