Whole blood from splenectomized subjects (n = 8) contained a substantial percentage of vacuolated ('pitted') red cells (34.7 +/- 8.3%), while blood from controls revealed none. The percentage of haemoglobin A1 (HbA1) had increased significantly compared with controls (p less than 0.01). Fractionation on cell density revealed that the number of 'pitted' cells and the HbA1 percentage were associated with increased cell density. Fractionation on cell volume showed that 'pitted' cells are equally distributed in fractions with varying mean cell volume (MCV) and that decreasing MCV was associated with a linear rise of HbA1. It appeared that, shortly after splenectomy (n = 4), 'pits' develop early in cell life and that also older cells, after previous splenic contact, are capable of pit formation. A positive correlation found between the number of 'pitted' cells and the percentage of HbA1 might point to an impaired release of HbA1, manifest in the presence of 'pits'. The increased percentage of HbA1 in whole blood from splenectomized subjects may thus be explained.