A novel version of a home-made hanging mercury drop electrode (HME) prepared in our laboratory is presented. Its main technical features are described, as well as the advantages it offers over the commercial ones. With this version the area of the electrode surface can be measured with great accuracy, and the reproducibility of the area from one mercury drop to another is better than 1 x 10(-3) cm(2), corresponding to less than 1% of the total amount of the surface area of an average mercury drop. The constancy of the area, for time periods of up to 90 min, and the reproducibility from one drop to another make this version of HME suitable for use in the analytical field in the study of adsorption or electron transfer phenomena when it is necessary to know the exact electrode surface area in order to determine surface density charge or differential capacitance values.