Domain structure changes in (1-x)Pb(Mg1/3Nb2/3)O-3-xPbTiO(3) have been studied by polarized optical microscopy. In the zero-field-cooled condition, increasing the x revealed systematic changes in the domain morphology from polar nanodomains for x<0.25, to fine crosshatched domains near the morphotrophic phase boundary (MPB), and to micro-sized domains for x=0.4. In the vicinity of the MPB, an applied dc electrical bias resulted in a change of morphology from fine crosshatched (rhombohedral phase) to thin-aligned striationlike (monoclinic phase) domains. The application of an ac electric field to the crosshatched domains resulted in irregular domain wall oscillations/relaxations and increased nonuniformity. (C) 2004 American Institute of Physics.