GPI and paroxysmal nocturnal hemoglobinuria: GPI (+) granulocytes had a higher proportion of apoptotic cells than GPI (-) granulocytes at 0 and 4 hours of culture. Co-culture with mononuclear cells increased the differential between apoptotic fractions in GPI (+) and GPI (-) cells. Percent apoptotic GPI(+) cells in PNH patients was higher than in healthy controls.