Abstract: A pipette pump for pipetting fluid includes an elongated hollow barrel and a pump mechanism at one end of the barrel. The pump mechanism includes a compressible portion which is actuated to fill the pipette barrel. Thereafter, the pipette barrel is vented to the atmosphere to bypass the pump mechanism such that the fluid in the pipette barrel is discharged by gravitational forces and atmospheric pressure rather than by actuation of the compressible portion of the pump mechanism. The pipette barrel may be repeatedly vented to discharge the contents of the pipette in a series of aliquots. The pump mechanism, when compresssed and not bypassed, provides rapid, positive displacement discharge of the contents of the pipette.