In interpreting peripheral blood films it is necessary to recognise extraneous cells that are occasionally present. These can include epithelial cells (either nucleated or not), endothelial cells and even subcutaneous fat cells. Noting the presence and recognising the nature of such cells is important, both because they may otherwise be misinterpreted as cells of pathological significance and because, in the case of fat cells, they may be sufficiently numerous to interfere with an automated count. These images show endothelial cells at low power (top) and high power (bottom). These cells tend to occur in loose sheets and are pleomorphic with round to oval nuclei and variably condensed chromatin. Nuclei may be irregular or grooved and some cells appear to be multinucleated.