The structure of diblock copolymer melts under a single external electric or shear field, as well as under combined orthogonal external fields was investigated using a cell dynamic system: The phase structure was determined by coupling the effects of the external: fields with the original structure of the bulk free of external fields. The single electric or shear field generated long-range cylinders in asymmetric A(4m)B(6m) diblock copolymers and distorted lamellae in symmetric A(5m)B(5m) diblock copolymers: Successive orthogonal shear followed by an electric external field generated long-range lamellae in symmetrical A(5m)B(5m), systems. However, the simultaneous orthogonal electric and shear fields could more easily form long-range lamellae than the sequential orthogonal fields. The dynamical processes in diblock copolymer melts under orthogonal fields have been also examined. (C) 2004 American Institute of Physics.