The invention concerns a diagnostic tape cassette comprising an analytical test tape (12), a supply spool (14) for winding off unused test tape (12) and a take-up spool (16) for winding used test tape (12), a housing (22) and a rotational lock (24) for the take-up spool (16) at least against inadvertent unwinding of test tape (12), wherein the rotational lock (24) has locking teeth (26, 28) disposed on both the housing (22) and the take-up spool (16), said teeth being shifted by an axial movement of the take-up spool (16) between a mutually engaged position and a release position.
