SummaryLow-calcium tetany and low-magnesium tetany in man are characterized by a repetitious myo-electrical activity.By comparison of electromyographical data obtained in hypopotassemia and alcalosis, we observe the repetitious activity of calcium tetany and magnesium tetany, together with a fibrillar activity (sometimes grouped in myotonic volleys). Repetitious activity is not arising when alcalosis disappears. Fibrillar activity and myotonic volleys disappear at normal potassemia.We conclude that myotonic volleys seem typical for hypopotassemia.