Concentrated suspensions of non-Brownian spheres dispersed in a Newtonian carrier liquid were placed under large amplitude oscillatory shear flow. It was found that the response wave forms consisted of a transient response after each reversal in the shearing direction, followed by purely viscous behavior. It was thought that rearrangements in the particulate microstructure could account for this transient response. Further, the characteristic strain for the microstructural rearrangement was found to be essentially independent of the oscillation frequency, and showed good agreement with the corresponding characteristic strain obtained from measurements of the transient response after shear reversal in continuous shear experiments. In addition, the fluidity in the oscillatory flow after the transient response was found to be higher than that in the steady flow case. This increase in fluidity was found to depend on the particle size dispersity, with the largest fluidity difference occurring with the monodispersed systems. (C) 2005 The Society of Rheology.