Poly(lactic acid) (PLA) is a biodegradable synthetic polyester with unique properties that make it an excellent candidate for biomaterial blends. It provides improved moisture resistance to blends with biopolymers and biodegradability/biocompatibility to blends with synthetic polymers, without impairing the useful properties of blend components. The successful development of materials from blends of PLA requires an understanding of the factors affecting the interfacial properties of such blends. In this work, the effect of temperature on the interfacial tension of PLA/ polystyrene (PS) blends was measured at 170-200 degreesC with the imbedded fiber retraction (IFR) method. IFR allows for the direct measurement of the interfacial tension of blends with high molecular weight/high viscosity components. In the temperature range studied, the interfacial tension of PLA/PS was independent of temperature and had a value of 5.4 +/- 1.3 dyn/cm. The interfacial tension was also calculated from the surface energies of PLA and PS with geometric mean (GM), harmonic mean (HM), and Antonoffs equations and from solubility parameters with the procedure of Luciani et al. IFR measured values were similar to those predicted by the procedure of Luciani et al. and Antonoffs equations, which gave 4.4 and 3.0 +/- 1.4 dyn/cm, respectively. The GM and HM methods predicted much lower values of 1.1 +/- 0.5 and 1.7 +/- 1.1 dyn/cm, respectively.