The effects of low-molecular-weight additives on the interfacial behavior of polymer blends have been studied experimentally and theoretically. The measured interfacial tension near the critical solution temperature T-c for poly(dimethylsiloxane)/poly(tetramethyldanylethylene) as a function of temperature is merely shifted by the addition of oligo(dimethylsiloxane) corresponding to the decrease of T-c, giving only a subtle adsorption effect in interfacial behavior. Theoretical calculations have also been carried out for polymer/polymer/additive ternary systems using the square-gradient theory (SGT) and the dynamic mean-field (DMF) calculation. The experimental results are quite consistent with theoretical predictions. Further theoretical calculations demonstrate that higher molecular weights and less miscibility with matrix polymers are most effective for a large adsorption of additives in the interface, leading to a large reduction of interfacial tension. SGT and DMF are found to predict almost the same interfacial tension and composition profiles in ternary polymeric systems. (C) 2001 Elsevier Science Ltd. All rights reserved.