Erythrocytes from patients with paroxysmal nocturnal hemoglobinuria are deficient in decay-accelerating factor (DAF), a factor called C8-binding protein or homologous restriction factor, acetylcholinesterase (AchE), and lymphocyte function-associated antigen 3 (LFA-3). These proteins share a common feature that glycan-inositolphospholipid anchors the protein to the membrane, suggesting that an abnormality related to this glycolipid causes multiple protein deficiencies. The relationship between the DAF, AchE, and LFA-3 defects was studied by fluorescent flow cytometric analysis. In five patients, DAF-negative erythrocytes were also AchE-negative. In three patients, a fraction of DAF-negative erythrocytes expressed subnormal levels of AchE, indicating that AchE was synthesized in these DAF-negative cells. Erythrocytes from the patients having DAF-negative, AchE-positive cells were separated according to density and analyzed for expression of DAF and AchE. Both proteins decreased with increase of cell density, suggesting that DAF-negative, AchE-positive cells become AchE-negative during erythrocyte maturation by losing AchE. A low level of LFA-3 was found on DAF-negative erythrocytes from one patient and decreased with erythrocyte maturation. These results support an idea that complete deficiency of glycan-inositolphospholipid-anchored proteins on erythrocytes could result from abnormally early termination of surface recruitment of these proteins, and subsequent dilution through cell divisions and loss from the surface.