Abstract: A test tube rack assembly including a test tube rack pivotally connected to a base having end support structure for allowing pivoting motion of the test tube rack with respect to a stationary base about a horizontal axis. A selectively actuable connector is affixed to at least one of the base end supports and includes a stud selectively engageable with one of a plurality stud receivers associated with the test tube rack for pivoting movement therewith. Each of the stud receivers defines a different angular position of the test tube rack with respect to the base. Preferably, a holder is disposed between the base and the test tube rack. A pair of holder end supports, comprising spring plates, have locking and alignment structure which mates with structure on the ends of the test tube rack to allow releasable, secure engagement between the holder and the rack.