1. A centrifugal packing technique has been used to investigate the effect of incubation on the flexibility of erythrocytes containing normal (Hb A) or sickle-cell (Hb S) haemoglobin. The effects on cell morphology and on the reversibility of morphological changes were also investigated.
2. The two types of cell reacted similarly to incubation. Sickling of the Hb S-cells was shown not to be responsible for the production of irreversibly deformed cells in these circumstances.
3. It is concluded that for both cell types the membrane inflexibility, cellular deformation and morphological irreversibility induced by the incubation were due to metabolic depletion.