An apparatus (1) for marking a laboratory sample carrier (2), includes a guide (5) configured to guide a sample carrier (2) from an entry location (6) to an exit location (7), and a print head (23) configured and positioned to mark a sample carrier (2) at a marking location (24) at a guide position intermediate the entry and exit locations (6, 7). The guide (5) is inclined such that a laboratory sample carrier (2) can travel from the entry to the exit locations (6, 7) under the influence of gravity. The apparatus (1) further includes a selectively deployable stop (41) for arresting the travel of a sample carrier (2) down the guide (5) at the marking location (24), the stop (41) being undeployable to allow the sample carrier (2) to travel from the marking location (24) to the exit location (7).