Modifications in the erythrocyte membrane protein band 3 seem to mark the cell for death. A decrease in band 3 high molecular weight aggregates (HMWAg) and a rise in its proteolytic fragments (Pfrag) were described for younger erythrocytes. The aim of this work was to study the band 3 profile as a marker of erythrocyte changes in pregnancy and postpartum. We performed a cross-sectional study in non-pregnant controls (n = 24), in women in the first (n = 64), second (n = 48) and third (n = 67) trimesters of gestation, and also in the puerperium (24-48 h after delivery; n = 32); we also carried out a longitudinal study (n = 23) during the three trimesters of normal pregnancy. We evaluated the band 3 profile (% of band 3 monomer, HMWAg, and Pfrag) and the membrane-bound haemoglobin. Total serum bilirrubin, glutathione peroxidase activity, red blood cell (RBC) count, haematocrit (Ht), haemoglobin (Hb) concentration, the haematimetric indices, and red cell distribution width were also evaluated. Similar results were found in pregnancy in both the cross-sectional and longitudinal studies. We found that the RBC count, Hb, and Ht decreased significantly in pregnancy and in puerperium. Band 3 profile in the first trimester of pregnancy, when compared with controls, presented significantly reduced HMWAg and increased Pfrag. Comparing the first with the third trimester, we found a significant reduction in band 3 and a significant rise in Pfrag. However, between these same periods, HMWAg did not decrease. Our data suggest band 3 profile as a marker of erythrocyte changes in pregnancy, which are independent of the 'physiological anaemia' of pregnancy. These changes suggest an increase in damaged RBCs, but also an increase in younger RBCs in the maternal circulation.