The clinic observations of three brothers presenting Dystrophia Myotonica (Steinert's disease) are reported. The patients presented wasting of several muscles and the mournful set expression of the face. By tapping some muscles (mainly the deltoides) with a percussion hammer, a weal was produced which slowly subsided. All the patients studied presented also atrophy of the testicles with azoospermia but without impotence; besides there was a peculiar cataract in all the patients, excessive secretion of tears and a mild mental deterioration. Attencion is recalled to some particularities of the observations, chiefly to the importance of electric changes (slow contraction, fibrillar reaction, etc). The changes of the electric excitability and the fibrillar contractions suggest the impairment of the cells of spinal cord's ventral horns.
