Abstract: A press-down valve is provided for medical instruments for suction and irrigation and a medical instrument having installed such a press-down valve. A valve stem is pressed permanently into a closure position via a pretensioned spring. For actuation, the valve stem is moved counter to the force of the spring via an actuation element, and, after release, the spring presses the valve stem back into the closure position. A catch mechanism is provided by means of which the valve stem can be locked in the open position only when the press-down valve has been removed from the medical instrument, and that, when it is installed in the medical instrument, the catch mechanism is automatically released and remains released.