The entropy theory of glasses is used to determine the glass temperature depression by a multicomponent low molecular weight plasticizer (diluent). The glass temperature, T-g, is calculated as a function of pressure, P, the mole fractions, m(i), of the plasticizers, and the degree of polymerization p. One finds, provided there is no phase separation, that to a good approximation, the initial glass temperature depression is a function of the total mole fraction of plasticizer. Moreover, the glass temperature depression for small plasticizer molecules is found to be nearly a universal function of the plasticizer mole fraction (it depends on no other plasticizer variable), and to vary inversely as the number of flexible bonds per monomer unit of the polymer. A useful approximation is found, gamma dT(g)/dm(1) = -3T(g), where m(1) is the total mole fraction of diluent on a per monomer of polymer basis, and gamma is the number of flexible bonds per monomer. Although these results agree with experimental data in the literature, a more definitive experimental test is needed.