The internal friction and dielec. losses of mixed Li-Na, Li-K, Li-Cs, Li-Ag, Na-K, Na-Cs, and Na-Ag metaphosphate glasses are related to the mixed alkali effect. The magnitude of the mixed peak correlates better with size differences than with mass differences. The intermediate temp. peak is treated as a mixed proton-alkali peak. The large mech. loss peak, appearing when the alkalies are mixed, was attributed to a coupled movement of dissimilar alkali ions and an explanation of the nature of this coupling is proposed. From this model it is predicted that mixed peaks can occur in any elec. insulating material contg. dissimilar charge carriers.