A sample rack for carrying a plurality of receptacles, wherein the receptacles may be of different sizes, said sample rack comprising: a receptacle holder comprising: a plurality of receptacle-receiving pockets; a receptacle positioning feature associated with each of said receptacle-receiving pockets; a resilient element associated with each of said receptacle-receiving pockets, wherein each receptacle-receiving pocket is configured to receive a receptacle and said resilient element is configured to urge the receptacle into said positioning feature to hold the receptacle in a fixed, predetermined position within said receptacle-receiving pocket; and a cover configured to be releasably secured to said receptacle holder, said cover comprising: opposed side walls (132, 134); a transverse wall extending between said side walls and including a plurality of spaced-apart receptacle access openings formed in said transverse wall, each receptacle access opening being associated with one receptacle-receiving pocket, wherein a portion of each side wall extends above said transverse wall and a portion of each side wall extends below said transverse wall; upper divider walls projecting above said transverse wall and extending across said transverse wall from one side wall to the other side wall with one upper divider wall disposed between each adjacent pair of access openings; lower divider walls projecting below said transverse wall and extending across said transverse wall from one side wall to the other side wall with one lower divider wall disposed between each adjacent pair of access openings; and a receptacle-retaining element (152, 154) associated with each receptacle-receiving pocket and configured to engage a portion of the top of a receptacle urged into the predetermined position within each receptacle-receiving pocket to prevent the receptacle from being lifted out of the receptacle-receiving pocket. a receptacle holder comprising: a plurality of receptacle-receiving pockets; a receptacle positioning feature associated with each of said receptacle-receiving pockets; a resilient element associated with each of said receptacle-receiving pockets, wherein each receptacle-receiving pocket is configured to receive a receptacle and said resilient element is configured to urge the receptacle into said positioning feature to hold the receptacle in a fixed, predetermined position within said receptacle-receiving pocket; and a plurality of receptacle-receiving pockets; a receptacle positioning feature associated with each of said receptacle-receiving pockets; a resilient element associated with each of said receptacle-receiving pockets, wherein each receptacle-receiving pocket is configured to receive a receptacle and said resilient element is configured to urge the receptacle into said positioning feature to hold the receptacle in a fixed, predetermined position within said receptacle-receiving pocket; and a cover configured to be releasably secured to said receptacle holder, said cover comprising: opposed side walls (132, 134); a transverse wall extending between said side walls and including a plurality of spaced-apart receptacle access openings formed in said transverse wall, each receptacle access opening being associated with one receptacle-receiving pocket, wherein a portion of each side wall extends above said transverse wall and a portion of each side wall extends below said transverse wall; upper divider walls projecting above said transverse wall and extending across said transverse wall from one side wall to the other side wall with one upper divider wall disposed between each adjacent pair of access openings; lower divider walls projecting below said transverse wall and extending across said transverse wall from one side wall to the other side wall with one lower divider wall disposed between each adjacent pair of access openings; and a receptacle-retaining element (152, 154) associated with each receptacle-receiving pocket and configured to engage a portion of the top of a receptacle urged into the predetermined position within each receptacle-receiving pocket to prevent the receptacle from being lifted out of the receptacle-receiving pocket. opposed side walls (132, 134); a transverse wall extending between said side walls and including a plurality of spaced-apart receptacle access openings formed in said transverse wall, each receptacle access opening being associated with one receptacle-receiving pocket, wherein a portion of each side wall extends above said transverse wall and a portion of each side wall extends below said transverse wall; upper divider walls projecting above said transverse wall and extending across said transverse wall from one side wall to the other side wall with one upper divider wall disposed between each adjacent pair of access openings; lower divider walls projecting below said transverse wall and extending across said transverse wall from one side wall to the other side wall with one lower divider wall disposed between each adjacent pair of access openings; and a receptacle-retaining element (152, 154) associated with each receptacle-receiving pocket and configured to engage a portion of the top of a receptacle urged into the predetermined position within each receptacle-receiving pocket to prevent the receptacle from being lifted out of the receptacle-receiving pocket.