The glycoprotein IIb, the alpha subunit of the platelet integrin GPIIb-IIIa, is a marker of megakaryocyte, but the stage of its expression during haematopoiesis remains controversial. We have examined the expression of GPIIb protein and alpha IIb mRNA in early human normal stem cells. We have purified stem cell expressing the CD34 surface marker (CD34+ fraction) and selected among this population quiescent cells (CD34+ MF(R) fraction). We have failed to detect GPIIb protein and alpha IIb mRNA in the pluripotential (CD34+ MF(R)) cells, even with polymerase chain amplification. Therefore alpha IIb transcription and GPIIb protein expression seemed to follow the commitment of the pluripotential cell in the megakaryocyte lineage.