The pattern of changes in brain-specific proteins mainly related to the synapses were studied in rats given electroconvulsive stimuli (ECS). One group was studied after three ECS per week for 4 weeks, another was further allowed a recovery period of 12 weeks. The experimental animals were compared with adequate controls. Brain-specific proteins were analyzed using crossed immunoelectrophoresis. The changes in the protein pattern after 4 weeks of ECS differed in the regions studied and are interpreted as follows: in the hypothalamus the amount of synapses seem to have increased, in the forebrain synaptic remodelling is under way and in the occipital cortex a delay in the neuronal development has been induced. The results further indicate an overall increased preparedness to meet the glycolytic demands accompanying seizure. Following 12 weeks of recovery a partial reversion of the induced changes was observed. The implication of the findings in relation to newer concepts of the working action of electroconvulsive therapy is discussed.