The transition from solid-like to liquid-like behavior of suspensions of monodisperse spherical particles in a Newtonian continuous phase with varying solid volume concentrations and particle sizes was investigated in rotational shear flows. It was found that the solid-liquid transition takes place in a relatively narrow shear stress range, where the corresponding shear strain,, and the shear rate, respectively, increase over some orders of magnitudes. Below the transition region the material behaves like a nonlinear elastic solid with an initial linear range, i.e gamma = f (sigma). The transition depends on the type of the shear loading and on the solid volume concentration. At high shear rates a nonlinear viscous behavior (gamma = f (sigma)) with a terminal Newtonian range gamma = sigma/eta was observed, if the solid volume concentration is below a critical value. Above this value the material behaves like a moist bulk solid material.