A carriage unit for sliding doors of building or furniture, comprising a stopping and damping device and a carriage which runs in a slide rail and which is designed to support and guide elements of sliding door panels along the rail, the carriage having an axis which supports an element of sliding door panels and which is perpendicular to a line of movement of the carriage along the rail, the stopping and damping device comprising a body mounted in the rail and a retaining device for retaining the carriage which runs in the rail the body is mounted on, which interacts with the retaining device and which guides and supports the element of sliding door panels, wherein the retaining device comprises: - a retaining lever connected to the body rotatably about an axis of rotation and movable about the axis of rotation between a first end position and a second end position; - elastic opposing means which are operatively interposed between the body and the retaining lever and which generate a reaction torque opposing the rotation of the retaining lever in a first direction of rotation from the first end position to the second end position; the rotation of the retaining lever in the first direction of rotation being started by the contact of a first lever arm of the retaining lever with predetermined portions of the carriage when the carriage approaches the body during its movement along the rail; during this rotation, the retaining lever being urged into and, under the action of the elastic opposing means, being caused to adopt, a retaining position on the carriage, preferably by reversing the direction of rotation, wherein: - the elastic opposing means comprise a helical spring mounted so it is compressed between the body and a second lever arm of the retaining lever, the helical spring being mounted with its own longitudinal axis transverse to the retaining lever and transverse to the second lever arm, the second lever arm being located on the side of the axis of rotation opposite the first lever arm; characterized in that: - the stopping and damping device being mounted in the rail, the longitudinal axis of the helicoidal spring is parallel to the axis of the carriage which supports the element of sliding door panels and perpendicular to the axis of rotation which, in turn, is perpendicular to a plane in which the element of sliding door panels lies. - a retaining lever connected to the body rotatably about an axis of rotation and movable about the axis of rotation between a first end position and a second end position; - elastic opposing means which are operatively interposed between the body and the retaining lever and which generate a reaction torque opposing the rotation of the retaining lever in a first direction of rotation from the first end position to the second end position; - the elastic opposing means comprise a helical spring mounted so it is compressed between the body and a second lever arm of the retaining lever, the helical spring being mounted with its own longitudinal axis transverse to the retaining lever and transverse to the second lever arm, the second lever arm being located on the side of the axis of rotation opposite the first lever arm; characterized in that: - the stopping and damping device being mounted in the rail, the longitudinal axis of the helicoidal spring is parallel to the axis of the carriage which supports the element of sliding door panels and perpendicular to the axis of rotation which, in turn, is perpendicular to a plane in which the element of sliding door panels lies. - the stopping and damping device being mounted in the rail, the longitudinal axis of the helicoidal spring is parallel to the axis of the carriage which supports the element of sliding door panels and perpendicular to the axis of rotation which, in turn, is perpendicular to a plane in which the element of sliding door panels lies.