Abstract: The operating mechanism of a tool retention and ejection mechanism for the spindle of a machine tool is located in an annular space between the spindle and the grill. A drawbar is slidably disposed in an axial bore formed in the spindle and is provided with a collet at the cutter end of the spindle for engaging a tool holder and drawing it into the socket of the spindle. The drawbar is shifted into its locking position by an annular array of balls that are forced against a bevel surface by a cam ring that is moved to a locking position by a spring. The bevel surface is formed on a ring that encircles the spindle and which is coupled to the drawbar by a crossbar that extends radially through the spindle. In order to increase the power available for releasing the mechanism, two annular pistons are provided in an annular cylinder disposed in the space between the spindle and the quill.