Abuse of growth hormone (GH) in sport is evidenced by customs and police, and more recently through testing in anti-doping laboratories. The popularity of GH among cheaters contrasts to the difficulty to prove performance-enhancing effects in controlled studies. Earlier results from replacement therapy in GH deficient adults indicated effects on muscle strength, which were not confirmed in meta-analyses. Even less evidence is available from healthy, trained adults. Obviously, it is impossible to mimic doses used by dopers in controlled studies. Changes in body composition induced by GH lipolytic actions could be helpful in some disciplines. Biochemical detection of doping with recombinant GH remained impossible for decades because of the short half-life in circulation and the similarity of pharmaceutical preparations to endogenous GH. The “marker method” uses changes in GH dependent biomarkers with longer half-lives, and some athletes have been banned because concentrations of IGF-I or P-III-P (a marker of bone and collagen turnover) were grossly elevated. High inter- and intra-individual variability of the biomarkers remains problematic. The “isoform-method” detects changes in molecular isoforms of GH occurring after administration of recombinant GH. This consists of the 22kD isoform only, while the pituitary secretes a wide spectrum of GH isoforms. A respective change in circulating GH isoforms can be measured by specific assays. Window of detection is limited, but targeted out of competition testing continuously detects cheating athletes. Associated sanctions have been upheld in front of the court of arbitration is sports, and the method is widely implemented today.