I have seen and experienced weakened reactions in MTS gel tests when I have pipetted cell and plasma straight down into the chamber with the Biohit pipette. Try this experiment: Center the tip of the pipette in the chamber opening. Pipet screening cells vertically into a gel tube chamber with enough force to eliminate the air-gap over the gel. Then, in the same manner, pipette QC material (dilute anti-D or other dilute antibody) into the cells. Do the same in the adjacent gel tube pipetting at and angle, preserving the air-gap. Mark each tube accordingly. Continue setting up tubes until two cards have been prepared. Incubate, spin and compare reactions. Walter