Abstract: The intracellular free Ca²⁺ concentration was measured in freshly dissociated brain cells prepared from neonatal rats using the fluorescent Ca²⁺ indicator Fura- 2/AM. Cytosolic Ca²⁺ concentration of resting cells was calculated to be 240±5 nmol/L. Depolarization with high K⁺ resulted in an over 100% increase in intracellular Ca²⁺ concentration, and this increase could be prevented or reversed by verapamil or nifedipine known to block voltage-sensitive Ca channels. These results suggest that the adoption of Fura- 2/AM method in freshly dissociated rat brain cells is a useful and relatively easily applicable technique for monitoring intracellular Ca²⁺ changes.