The effect of cadmium on spectral EEG parameters of the hippocampus, somatosensory, visual and auditory cortical zones, as well as representation of wakefulness, slow-wave sleep and paradoxical sleep has been studied in the diurnal cycle of Wistar rats. It was shown that single injections of cadmium chloride (3 mg/kg, intraperitoneally) induce significant changes in the structure of wakefulness-sleep cycle, whereas no reliable qualitative changes in EEG parameters were observed. After long-term (9 days) administration of cadmium chloride (1.5 mg/kg, intraperitoneally), epileptiform activity was noticed in the EEG pattern, whereas predisposition of animals to audiogenic seizures increased.