A scanning tunneling microscope suitable for very low temperatures has been designed, and preliminary testing has been
carried out. In order to improve cooling and temperature uniformity the instrument is arranged for operation immersed in
the 3He-4He mixture inside the mixing chamber of a small dilution refrigerator. A discussion of the specific problems
present in the design of this kind of an instrument is given as well as a description of our design. Special attention is given to
the vacuum sealing and vibration-damping solutions required.