Five cases of myoclonic cerebellar dyssynergia and 3 cases of myoclonic epilepsy are reported. The authors make a revision of the problem, specially about myoclonic manifestations. Myoclonus is analyzed pathologically and electroencephalographically. From the pathological point of view the dynamic feature of the lesions is emphasized, so that, at a given time, it is possible to have a histological picture that is in progression. This explain the variety of pathological descriptions in the literature, even though all of them have a common anatomical basis, the olivodentorubral triangle being the site of the lesions producing myoclonus. The authors try to explain myoclonus as caused by lesions of one or several points in this triangle, emphasizing the importance of the reticular formation of the brain stem. It is the opinion of the authors that the electroencephalographic patterns agree with the pathological findings in what concerns the site of the lesions. The authors verified that, by making an electroencephalographic record with the aid of a curare-like drug (succynilcholine chloride), which suppresses the muscular component, the morphology of the waves is changed and the frequency of the paroxysms is diminished. The decrease in the frequency of discharges is interpreted as being the result of a greater number of stimuli directed to the motoneurons than to the cerebral cortex, starting in subcortical structures which are responsible for the myoclonus; during the action of succynilcholine chloride only the cortical discharges, which are rarer, would be registered. Or else, this curare-like drug would have an anticonvulsivant action which has not yet been demonstrated. Although both diseases, in some cases, have a very similar clinical picture, it is possible, on histopathological grounds, to regard them as two distinct clinical conditions.