The rheological properties of setting acrylic bone cements were examined with a rotational cone and plate viscometer. The cements were tested over two orders of magnitude of shear rate to determine the nature of any non-Newtonian flow behavior. All three cements behaved with moderate pseudoplasticity (i.e., shear thinning) during setting, suggesting the use of higher pressures during administration for better flow and penetration. The low viscosity brand was found to be nearly one-half as viscous as the conventional cements during the working time (i.e., 2-5 minutes). A series of sieving experiments were performed to determine the particle size distributions of the powder components. Statistical analysis (chi square) showed the cements to have different distributions, with the low viscosity brand containing a larger proportion of smaller polymer particles. This difference is thought to contribute to the lower viscosity of this cement.