A connection unit for connecting fluid lines, including a plug-in unit connectable to a first fluid line not belonging to the connection unit, defining a first fluid flow channel in its interior, and a receiving unit connectable to a second fluid line not belonging to the connection unit, defining a second fluid flow channel in its interior. The plug-in unit and the receiving unit are connectable to establish a fluid connection between the first and second fluid flow channels. The connection unit also includes a release element transferrable from a holding state to a release state upon insertion of the plug-in unit into the receiving unit up to a predetermined depth, and an indicator element formed separately from the release element and locked by the release element in the holding state. The indicator element is detachable from the connection unit when the release element is in the release state.