The effect of repeated electroconvulsive shock (ECS) on the activities of the three enolase isoenzymes present in rat brain: neuron specific enolase (NSE), non-neuronal enolase (NNE) and the hybrid enolase was investigated in piriform cortex. The activities were estimated on isoenzymes separated by agarose gel electrophoresis. Whereas the specific activities of NNE and hybrid enolase were unchanged in piriform cortex or ECS-treated rats the specific activity of NSE was increased by 16.3 percent (P < 0.02). The brain enolase isoenzymes are dimers of alpha- and gamma-enolase subunits. The calculated ratio between the gamma-subunit present in both NSE and hybrid enolase and the alpha-subunits present in both NNE and hybrid enolase was increased by 11.7 percent in piriform cortex of ECS-treated rats (P < 0.05). Previously, it has been shown that the gamma-subunit is only expressed in neurons whereas the alpha-subunit is expressed in both neurons and glial cells. The selectively increased expression of the enolase gamma-subunit in ECS-treated rats might either reflect an increased transcription of a whole group of neuronal genes or rather the trophic role of NSE in ECS-enhanced synaptic remodelling of the rat brain.