Abstract: An apparatus for adjusting the position of the slats of Venetian blinds comprises means for packing and extending the slats, means for adjusting the angular position of the slats and lost-motion means interposed functionally between the said packing and extending means and the said adjustment means in such a way as to lock the said Venetian blind adjustment means after a predetermined number of rotations of an actuating shaft. The lost-motion means comprise three toothed elements in functional sequence, a first one of which is functionally connected to the said slat packing and extending means and a third one of which is functionally connected to the said adjustment means. The toothed elements are housed inside each other.