In a blood smear, erythrocytes (red blood cells, RBC's) are the most common cell. They appear as eosinophilic discs with a dark rim and a light center. This is a result of the biconcave shape of the cells, which are thinner in the center and thicker around the edges. RBC's also lack a nucleus. During the air drying process that is part of preparing a blood smear, RBC's are not flattened as much as white cells, but they may become distorted from their normal discoidal shape.

Stain = Wright's Blood Stain.