Alignment by an electric field was obtained for a variety of particles dispersed in photopolymerizable fluids. The particle shapes studied were irregular, spherical, rhombohedral, rod-like (fibres), and platelet. The sizes ranged from sub-micrometres to tens of micrometres, a nd the dielectric constants of the particles varied from less than that of the liquid matrix to very much greater than that of the matrix. Polymerization or hardening of the matrix was possible at room temperature, required only a few seconds, and the aligned structures obtained were able to be examined by both light and scanning electron microscopy after fracture or sectioning. Nominally equiaxed particles, containing a statistical proportion of non-equiaxed particles, could be completely aligned at 48 vol % concentration in a fluid having a viscosity of about 2.5 Pa s, but at 57 vol %, the mixture behaved as a paste, and only particle rotation and local rearrangements were possible. The rate of alignment seemed to depend generally on the magnitude of epsilon(1)(a beta)(2), where epsilon(1) is the relative dielectric constant of the liquid resin, a is the particle radius, and beta is the particle dipole coefficient given by (epsilon(2) - epsilon(1))/(epsilon(2) + 2 epsilon(1)), where epsilon(2) is the relative dielectric constant of the particles. epsilon(1)(a beta)(2) emphasizes the importance of particle size a nd the relative unimportance of the particle dielectric constant for alignment, except when epsilon(2) approximate to epsilon(1). Platelets were more rapidly aligned than fibres.