Abstract: A utility knife has two shells that are pivoted or hinged to each other at one end to permit opening the knife handle formed by the shells for insertion or replacement of a knife blade. The two shells are interlocked with each other by a latching mechanism, including a stationary section in one shell and a rotatable section in the other shell. The rotatable section has a spring elastic bail that engages the stationary section and an operating member for disengaging or engaging the rotatable member from the stationary stop bar. In the interlocking position the operating member is recessed in a recess in the surface of one of the shells. When the knife is used, the operator's hand provides additional safety by keeping the operating member in its recess and thus the two shells interlocked.