A device for evaporating metals by electron beam bombardment within the electron microscope has been developed which operates without loss of image resolution or stability. This device is particularly applicable to dynamic studies of nucleation and growth of metallic films characterized by unusually high purity and/or high melting points. A hanging drop of molten material, formed by bombardment of the end of a vertical wire by a focused beam of 2–5 kV electrons, provides a controllable source of pure metal vapor.