Current anti-doping work includes the athlete biological passport in which individual changes in blood parameters are monitored longitudi- nally. These may be altered by alterations in plasma volume (PV) unrelated to doping practice. PV variations and haematological variations in conjunction with hormonal changes in active women taking oral contraceptive pill (OCP) are largely unknown. Data will be discussed from recent studies where measured PV variations using a validated carbon monoxide rebreathing method and are correlated to changes in haematological biomarkers (e.g., hemoglobin concentration ([Hb]), reticulocytes concentration, Transferrin (sTFN), ferritin (FERR), albu- min (ALB), calcium (Ca), creatinine (CRE), total protein (TP), and low-density lipoprotein (LDL) in women taking OCP over a duration of 8 weeks. Data will be presented in context of other non-doping activities that may affect plasma and red blood cell volume and thereby potentially influence the ABP.