A new grinding machine for preparing thin undecalcified bone sections after methylmethacrylate embedding is described. About 20 rather small bone sections can be ground at the same time; bigger specimens, up to 8 cm of length, are allowed. Bone sections are mounted on a cylindrical specimen holder by an adhesive film. Then the final thickness of the sections is exactly adjusted by screwing three rubies out of the holder’s bottom. Now the prepared holder is set in a guide ring on a turntable carrying a rough ended glass plate. The desired thickness of the sections is reached as soon as the three rubies touch the glass surface. The variation in the thickness of the sections is less than ± 3 μm. The machine is simply constructed, easily to handle and rapidly to cl