Cells which, accord­ing to cur­rent under­stan­ding, deve­lop into all the cells found in the blood – ery­thro­cytes, leu­ko­cytes or throm­bocytes. In adults, they are found almost exclu­si­ve­ly in the bone mar­row. By pre­pa­ring the donor with medi­ca­ti­on, stem cells can be flus­hed in lar­ge num­bers into the nor­mal bloo­d­stream and then extrac­ted from the peri­pheral blood.