The world of doping and anti-doping in sport is an ongoing race between those who want to gain a performance advantage by using prohibited substances or methods and those who want to keep the sport clean. Sophisticated doping often involves substances that are difficult to detect, which presents both scientific and legal challenges for implementing new detection methods. This article provides an overview of legal considerations in anti-doping procedures that may apply to the use of the marker method for the detection of Human Growth Hormone. In cases where the blood markers IGF-1 and P-III-P indicate use of exogenous growth hormone, reference to positivity criteria and laboratory uncertainty measurements would assist anti-doping adjudicative bodies in concluding, to their comfortable satisfaction, that a positive test has been established. Use of established positivity criteria and laboratory uncertainty measurements place the application of the marker method for growth hormone within the existing, accepted legal framework for evaluating an Adverse Analytical Finding.