The MS1 chamber has been designed for use with fixed-stage upright-type microscopes. The particular feature of this chamber is the profiled contour that allows the microscope objective to sweep across the preparation when changing magnification, without having to adjust the focusing. In this way the specimen and any pre-positioned microelectrodes remain par-focal. This is particularly useful for confocal microscopy where it is the intention to combine electrophysiology and precise localization of structures (Emptage, Bliss & Fine, 1999). The design also allows for movement of objectives that swing from front to back.