Forty-two patients with myoclonic manifestations (especially during subacute sclerosing panencephalitis (SSPE)) were studied. The multidimensional investigations pointed out that myoclonias produce several EEG and polysomnographical perturbations: 1. Sleep disorganization; 2. Appearance of the myoclonic jerks in wakefulness (especially) and in some sleep stages; 3. Some electroclinical discordances; 4. A great variability of the myoclonias during some sleep stages; 5. EEG cortical mappings showed individual variabilities of Radermecker complexes.