This report describes recent efforts to modify, test, and evaluate an experimental online database consisting of 15 vendor-supplied, controlled subject vocabularies or thesauri. The experimental database, called the Vocabulary Switching System (VSS), is designed to enhance search strategies and ultimately retrieval performance for users of online bibliographic databases by integrating vocabularies into common VSS files, thereby allowing the user access to about 315,000 possible search terms. VSS assists users with free-text or controlled vocabulary searches and single or multiple database searches. Work described includes: (1) evaluation of numerous switching strategies against the 15 resident vocabularies of VSS; (2) controlled experiments involving end-users and intermediaries; (3) system redesign and current status; (4) system testing and evaluation; (5) results of a 1983 survey of online users and comparison with a similar 1979 survey; and (6) conceptual designs for a future switching system. Numerous tables, figures, and appendices are provided. (THC)