This paper describes a lubricant evaluation method for fluid dynamic bearings (FDBs) using TOF-SIMS. By using this method, we found that worn metal elements generated both from spindle and bearings have substantial influences on lubricant degradation. TOF-SIMS is useful to compare the effects of bearing materials and operating conditions on oil degradation, and the lubricant quality can be judged by this technique. (C) 2002 Elsevier Science B.V. All rights reserved.