A coupling for pressure lines, having a housing (10) which has a continuous conveying duct (12) for a pressurised medium and can be connected by one end to a pressure source and attached by the opposite end to a connection nipple (30), and having retaining jaws (136) which are arranged around the mouth of the conveying duct opening into the connection nipple (30) and which can be fixed by a locking mechanism in a position in which they engage around the connection nipple (30), in which the retaining jaws (36) are each supported on a pivot bearing (38) and have, at the end remote from the connection nipple (30), beyond pivot bearing (38), an actuating arm (42) which can be actuated, in order to close the retaining jaws (36), by a piston (44) subjected to the pressure of the medium.