Abstract: A system comprising a tray and methods of loading and unloading units for sample racks. The system provides a tray for loading and unloading of samples to a system, wherein the tray comprises a base plate comprising on its upper surface a longitudinal extending guiding rail which is arranged closer to one of the two longitudinal sides of the tray, wherein the tray comprises at least one element that is configured to extend through an opening in the upper surface of the base plate, when the tray is lifted from a surface. Further, a system, comprising a tray as described above; and at least one rack comprising on its lower surface an acceptance slot configured for accommodating a guiding rail of the tray, and a loading area comprising two toothed conveyer belts arranged in a distance corresponding to the trays width.