The exchangeable pipette tip assembly (3) is seated on the pipette body, and has the ejector push (6) linked to the ejector (8), while the ejector push button (6) has the push button toothed bar (9), and the ejector pusher (7) has the pusher toothed bar (10). Inside the pipette body the push button toothed wheel (11) is disposed, which is engaged with the push button toothed bar (9), and the pusher toothed wheel (12), which is engaged with the pusher toothed bar (10), while both toothed wheels (11, 12) are interconnected so that they make the same rotational movement around their common axis (13) of rotation rigidly fixed with respect to the handle (1).