Ion selective microelectrodes (ISMs) have been used extensively in neurophysiological studies. ISMs selective for H⁺ and Ca²⁺ are notable for their sensitivity and selectivity, but suffer from a slow response time, and susceptibility to noise, owing to the high electrical resistance of the respective ion exchange cocktails. These drawbacks can be overcome by utilizing a "coaxial" or "concentric" inner micropipette to shunt the bulk of the ion exchanger resistance. This approach was used decades ago to record extracellular [Ca²⁺] transients in cat cortex, but has not been subsequently utilized. Here, we describe a method for the rapid fabrication of concentric pH and Ca²⁺-selective microelectrodes useful for extracellular studies in brain slices, or other work in vitro. Construction was simplified compared with previous implementations, by utilizing commercially available, thin-walled borosilicate glass, drawing an outer barrel with a rapid taper (similar to a patch pipette), and by employment of a quick and reliable silanization procedure. Using a piezoelectric stepper to effect a rapid solution change, the response time constants of the concentric pH and Ca²⁺-electrodes were 14.9 ± 1.3 and 5.3 ± 0.90 ms, respectively. The use of these concentric ISMs is demonstrated in rat hippocampal slices. Activity-dependent, extracellular pH and [Ca²⁺] transients are shown to arise 2 to 3-fold faster, and attain amplitudes 2 to 4-fold greater, when recorded by concentric vs. conventional ISMs. The advantage of concentric ISMs for studies of ion transport and ion diffusion is discussed.