A system includes a reagent pack input carousel, a carousel frame supporting the carousel, and a track on which the carousel frame is supported for movement of the carousel into and out of an instrument in drawer-like fashion. The carousel is rotatable about an axis of rotation and includes a plurality of reagent pack input stations arranged about the perimeter of the carousel. Each input station is adapted to carry a reagent pack, and the input stations are oriented at an angle with respect to a radial orientation relative to the axis of rotation. Each input station includes an alignment block located at a radially inner end of the station, and the block is received within a recess formed in an end of the reagent pack placed in the station to align and position of the reagent pack within the station.