We have demonstrated simultaneous measurement of the membrane potential and cytoplasmic free Ca²⁺ concentration ([Ca²⁺]_i) by utilizing a dual-laser flow cytometer in embryonic rat hippocampal cell suspensions. Veratrine, a Na⁺ channel activator, induced both membrane depolarization and elevation of [Ca²⁺]_i. These actions of veratrine were all reversed by the presence of tetrodotoxin (TTX). These findings suggest that Na⁺ channels are functionally expressed in the cells and the activation of Na⁺ channels increases [Ca²⁺]_i. The usefulness of the flow cytometric analysis in elucidating the expression of membrane functions in the embryonic central nervous systems (CNS) is discussed.