The paper describes the use of electrolytic-tank techniques for an initial determination of the electric fields in transformer-bushing insulators. The compound dielectric in the bushing is simulated by means of an electrolytic-tank model having watertight compartments each holding an electrolyte whose conductivity corresponds to the permittivity of the dielectric material. For this purpose, an interface boundary consisting of individual loops of fine copper wire was developed to conduct the electric current from one compartment to another. A 12ft-long electrolytic-tank rig was specially built to accommodate a full-scale bushing model. Various design configurations were investigated, and it was shown that, for example, for a 400kV bushing, the desired performance improvement could be achieved by inserting low-permittivity sleeves in the oil channel.