An automatic system based on the use of a PC-compatible computer was developed for the implementation of coulometric titrations by release of EDTA from its Hg complex on electrochemical reduction of the Hg2+ ion. A variety of indicators electrodes were assayed to obtain potentiometric titration curves. The method thus developed allows the straightforaward, convenient determination of Ca and Mg and was applied to the analysis of various real samples with good results.