Simultaneous electrical and rheological measurements (ERM) on polymer melts were introduced in 2004 to study properties of composites containing carbon nanotubes [1]. Since then these measurements have become a useful and sensitive tool to follow morphological changes in conductive polymer composites induced by a well-defined mechanical deformation. From an evolution of the electrical conductivity during a deformation one can draw conclusions regarding destruction and/or agglomeration of particle structures dispersed in the melt. Simultaneously, the effect of these structural changes on rheological properties of the composite is evaluated. In this contribution the experiments performed on composites with carbon nanotubes are briefly summarized [2]. Electrical and rheological behaviour of composites with carbon black under oscillatory and creep deformation is presented. Novel electrical-rheological measurements on polymer melts in elongation are discussed as well. Finally, opportunities of ERM in studies concerning with morphology development in filled polymer blends are discussed. [1] Kharchenko SB, Douglas JF, Obrzut J, Grulke EA, Migler KB. Nat. Mater. 2004;3(8):564-568. [2] Alig I, Pötschke P, Lellinger D, Skipa T, Pegel S, Kasaliwal GR, Villmow T. Polymer 2012; 53: 4.