A freeze dryer (10) comprises a chamber (12) having a rectangular slot through which vials are inserted into the chamber (12). An assembly for loading the chamber (12) comprises a bar (32) extending across the slot to engage vials to be inserted into the chamber (12). The bar (32) is attached to a mechanism (34) for moving the bar (32) laterally into and out from the chamber (12). In a retracted position of the bar (32), at least part of the mechanism (34) is wound around a sprocket (106). Rotation of the sprocket (106) unwinds the mechanism (34) to move the bar (32) into the chamber (12).