As annexin A7 is a component of red blood cell vesicles we studied the consequences of the loss of the protein in the anxA7-/-mouse for red blood cell morphology and osmotic resistance. In a standard 'blood smear' we did not note a deformation of the cells, however dark field microscopy revealed changes in shape and diameter of the anxA7-/-red blood cells. They had a statistically significant larger cell diameter of 6.0 μm compared to wild type with 5.7 μm (p = 0.015, n = 40), a remarkably lower emphasized central impression and a more flat shape (Fig. 4). No significant change in the mean corpuscular volume (MCV) was measured with the ADVIA 120 cell counter.