An experiment was designed to determine whether speech input is a valuable alternative or addition to manual input. Subjects used both speech and mouse input for control purposes in a document-annotation system. Speech recognition was realized by a speaker-dependent speech-recognition board. In separate sessions, subjects used either a mouse or speech interface, and comparisons were made between the two media in performance speed, number of commands, and number of errors. In a third session, subjects were free to use either input medium, and measures included both objective (usage) and subjective (questionnaire) preferences for the two media. The main results were that: (1)9 out of 24 subjects used speech more than the mouse when they were free to use both; (2) 21% of the subjects preferred speech control, because it allowed other devices to be operated manually; and (3) 37% of the subjects preferred to control the system with both input devices available. Speech can be a valuable addition to other input media enabling users to adapt their choice of media to specific task situations.