A simple and inexpensive method for constructing a double capillary was developed for preparing a self-filling glass microelectrode. The modified method uses a thin capillary instead of a bundle of glass fibers and fuses it to the outer capillary wall with flame before pulling the latter with a puller. The validity of the new electrode was proven by measuring the proximal cell PD of the rat kidney slices (mean of the stable cell PDs lasting longer than 30 min,--69 mV). A semifloating electrode was modified from the original floating electrode to be applicable to the in vivo kidney preparation whose pulsatile and respiratory movements had hindered yielding a stable cell PD. This electrode is constructed simply by replacing the shaft of the Ling-Gerard glass microelectrode with a length of flexible silcone-rubber tubing. The cell PD recorded by this electrode is found to be more stable and can withstand minor tissue distortion in mammalian kidney cells in vivo and also in such a contractile tissue as the secretory coil of the eccrine sweat gland.