The changes in aldehyde dehydrogenase(ALDH, E.C. 1.2.1.3.) activity in neurons and astrocytes isolated from rat brains were investigated after administration of ethanol and Korean red ginseng(Panax ginseng C.A. Meyer) saponln. The cerebral ALDH activity with acetaldehyde and Propionaldehyde was higher in the white matter than in the gray matter. However, using indole-3-a-cetaldehyde and 3,4-dihydroxyphenylacetaldehyde as substrates, there was no significant difference in activity between two regions in cerebrum. In ethanol treated group, ALDH activity with all the substrates in the gray and white matter was lower than in normal group. In ethanol-saponin treated group, the enzyme activity in the white matter remarkably Increased. The ALDH activity in neurons isolated from cerebral cortex in ethanol-treated group was lower than in normal group. In ethanol-saponin treated group, neuronal ALDH activity with propionaldehyde was significantly recovered but not with Indole-3-acetaldehyde. In astrocytes, although the ALDH activity with propionaldehyde in the ethanol-treated group was not changed as compared with normal group, considerable increase in activity was found in ethanol-saponin treated group. These results suggest that Korean red ginseng saponin may protect the neuronal functions from the toxic effects of acetaldehyde derived from ethanol by stimulation of ALDH activity in astrocytes surrounding nerve cells.