Preliminary studies have been made on the use of the modified axial lead system in infancy and childhood. A highly significant correlation between internipple distance and height suggested that internipple distance be used as an index for the selection of a template to facilitate placement of the chest electrodes (Z and X). A series of 4 triangular templates was designed. The use of a template one size too large or too small was shown not to lead to any significant error in waveform measurement. A further study showed that the reference level for the application of the praecordial electrodes should be the 5th intercostal space as for adults, but that no serious diagnostic error was likely to arise if the 4th or 6th intercostal space was chosen by mistake. A study of the Frank lead system suggested that the use of the 5th intercostal space as a reference level was more appropriate than the 4th intercostal space, which is generally adopted by users of that system. The conclusion reached was that the axial lead system is the preferred orthogonal lead system for children, with templates for 4 ranges of internipple distance (less than 10 cm; 15 to 20 cm; and less than 20 cm--adult build) being proposed to simplify electrode placement.