A novel technique that involves a spinning drop apparatus has been used to measure the interfacial tension of polymer melts on the basis of the shape of two colliding droplets. The technique combines the advantages of equilibrium techniques (accuracy and straightforward analysis) to a speed of measurement that is equal or faster than dynamic methods. For melt viscosity in the order of 10(4) Pas experimental time is in the order of 30 min. This is independent of viscosity ratio and interfacial tension itself, giving scope for investigating the effects of compatibilisers. Furthermore, the interfacial tension measurement is incorporated in a coalescence experiment. For the model systems chosen (PS/LDPE and PS/LLDPE) commercial polymers were shown to have reduced interfacial tension and increased scatter due to additives. When the polymers were purified the interfacial tension rose significantly.