The interfacial tensions between BPA polycarbonate (PC) and a series of styrene-acrylonitrile (SAN) blends having S/AN ratios varying between 100/0 and 60/40 (wt%) have been determined by measuring capillary thread breakup rates at 200-degrees-C. A distinct minimum in the interfacial tension is observed close to the SAN composition reported to show maximum miscibility with PC. For the case of PC/PS, the measured values are compared with those calculated from published studies on PS/poly methyl methacrylate (PMMA) and PC/PMMA.