Workstations are becoming more commonly used in medical environments, and are being used increasingly for viewing medical images. In most clinical environments, counter and wall space is not readily available, and there is a strong motivation to make the equipment small, while making the displayed images as large as possible to preserve image detail. This precludes the use of a separate text monitor for user interaction, and any menus or displays on the image monitor use valuable space -- pixels backed up with 256-shade grayscale capability. We have developed a method for user interaction which requires essentially no screen area for permanent menus, but uses much of the image screen for `invisible' menus -- menus which are in windows which are always open (active) but only obscure the underlying image for the small portion of time that they are actually in use. These invisible menus respond to movements of the mouse, and become visible when the mouse is moved into the window which holds the menu. The menu becomes invisible again after a period of mouse inactivity. Because these windows are always active, a given item may be selected multiple times by simply pressing the mouse button repeatedly. This `type-ahead' capability is not normally available on systems which do not include a keyboard, and may be easily used for common repetitive functions, analogous to pressing the NEXT IMAGE key multiple times. This invisible window concept can also be used to display analysis results, so that the results do not cover any of the active image area, but are immediately available for on-screen viewing.