Low ionic strength extraction (37 degrees C, 30 min) of ghosts from PK-deficient erythrocytes provided crude spectrin extract. No significant differences in the extract composition compared to normal donors were observed. The reticulocyte-dependent spectrin extractability was found among the subjects with PK-deficiency anemia. Likewise ATP-depletion affects spectrin extractability and also leads to the adsorption of cytoplasmic protein MW 50,000 to the reticulocyte membrane. The measurement of membrane fluidity using the fluorescence probe DPH did not reveal significant alterations in the moiety of integral membrane constituents.