Abstract: A fraction collector includes a rack-holding tray mounted on a base which houses a drive mechanism for actuating rack shifters, the tray carrying twelve three-test-tube racks or twenty five-test-tube racks in two staggered rows. A rack adapted for carrying n test tubes is provided on a bottom side with n projections spaced along the length of the rack by a distance equal to the quotient of the rack length divided by n, the projections coacting with shifters in the form of vertically extending fingers reciprocatably mounted at opposite ends of the base for pushing racks in n incremental steps from one row to another. Each rack further includes a pair of additional projections for cooperating with two row shifters to push a row by one rack width upon the transfer of a rack to this row from the other row; these additional projections are spaced by pre-established distances from the long sides of the racks to facilitate the movement of a rack row by exactly one rack width.