It's time to start talking about some of the terrible things you can do to your own body, like blood doping. We'll start by explaining the structure and function of your erythrocytes, and of hemoglobin, which they use to carry oxygen. We'll follow the formation and life cycle of a red blood cell, including how their levels are regulated by EPO and their signalling molecules. We'll wrap up by looking at how blood doping works and how it is truly a recipe for disaster.