The Athlete's Biological Passport (ABP) is an evaluation of hematological parameters, hemoglobin (Hb), reticulocytes (Ret), and their combination in the OFF-score. Recently, the Court of Arbitration for Sport accepted it as a suitable indirect method for detecting blood doping. There are various topics which are not defined and scientifically completely explained in ABP, limiting its effectiveness as evidence and as suspect of blood manipulation. The data source the ABP used for designing a profile is unclear. The variance used for cyclists is not correct. The covariables which should be calculated together with the measures of Hb and Ret are not always considered in the statistical program. The pre-analytical warnings for correct and valid collection, transport, and storage of the specimens are not assured. Quality control of the instruments is not completely assured. Analytical variability is not appropriately considered in the program. The seasonal changes of the hematological parameters, due to training and competitions, are not calculated. Statistical analysis, based on a Bayesian-like program, not available to the scientific community, does not follow the classical decision-making approach of medicine and science. The ABP needs of additional evidences and of scientific debate.