Grain size and lattice distortions as a function of milling time have been determined using X-ray peak broadening analysis and Brunauer-Emmett-Teller (BET) measurements. The grain size decreases from 0.22 mum in unmilled samples to 0.06 mum at 25 h milling time. Prolonged milling produced no further decrease of the grain size. The unmilled powder contained lattice distortions of 0.06%. During the first 25 h of milling only small changes of the lattice distortions occurred; longer milling times resulted in a rapid increase of the lattice distortions. At 47 h of milling, the lattice distortions had increased to about 0.11%. The results obtained by BET measurements agreed well with those obtained by X-ray analysis. No anisotropic grain size decrease was indicated during milling.