A surgical instrument for use in open surgery has two gripping limbs and a blocking element that releasably locks the gripping limbs relative to one another. The blocking element has a female locking assembly and a male locking assembly. The female locking assembly has a mechanical control device for locking and releasing a locking portion of the male locking assembly. A mechanical control assembly is assigned to the male locking assembly and moves the locking portion of the male locking assembly out of an end position that defines a neutral position into an end position that defines a functional position and, conversely, out of the end position that defines the functional position into the end position that defines the neutral position. The control assembly includes securing elements that secure the locking portion in both end positions.