Performance enhancing drug (PED) use is a historic issue at the highest levels of professional competition, driving use in young amateurs and compromising the healthfulness of sport. Legal criteria for detecting PED use in athlete’s urine and blood have been in continuous development for 40 years. Illicit use of endogenous substances such as testosterone cannot be established by their presence in fluids. High precision isotope ratio mass spectrometry (IRMS) can distinguish between endogenous and exogenous steroids by measurement of 13C/12C to 5 significant figures, enabling study of variability in isotope ratio due to natural processes. Among other strategies, the 2006 Tour de France first finisher Floyd Landis used steroids, and apparently methods to defeat doping detection. IRMS of urinary testosterone metabolites demonstrated doping to high legal certainty in widely publicized hearings in 2007 and 2008. Those verdicts in part led to Lance Armstrong’s later admission of doping. Known and never before revealed reflections on the chromatography and IRMS of the Landis case will be discussed, as well as the current state of doping control and detection.