Abstract  Combining voltage and Ca2+ imaging allows the correlation of electrical and chemical activity at sub-cellular level. Here we describe a novel apparatus designed to obtain simultaneous voltage and Ca2+ measurements with single-trial resolution from sites as small as a few microns. These measurements can be obtained with negligible optical cross-talk between the two signals and negligible photo-damage of the preparation. The capability of the technique was assessed recording either from individual neurons in brain slices or from networks of cultured neurons. The present achievements open the gate to many novel physiological investigations requiring simultaneous measurement of voltage and Ca2+ signals.