MCp could be immunomagnetically isolated from the blood after mast cell depletion of the peritoneal cavity . Blood was collected by cardiac puncture from nondepleted animals and animals whose peritoneal cavity had been depleted of mast cells by distilled water. By 12 hours after depletion it was possible to isolate MCps from cardiac blood. Only MCps could be isolated from cardiac blood using immunomagnetic beads conjugated to mAbBGD6. Mast cells were isolated from the blood using magnetic beads conjugated to mAb BGD6. The number of cells free or attached to the magnetic beads was determined by counting the cells in a hemocytometer. A minimum of 10 animals were used per time point. Data is expressed as the number of mast cells/108 blood cells ± S.D.