Thanks to the very successful Human Genome Project and the identification of genes involved in genetic disease, we now have the ability to treat many conditions. However, the identification of the genes which code certain phenotype characteristics has opened the way for abuse in the fields of sport and physical exercise. The principles of gene therapy and the ways in which genes are transferred have completely been copied from gene therapy and are now being used to increase the physical abilities of athletes. The genes most frequently used by athletes include: the the ACE gene, the ACTN3 gene, myostatin, the erythropoietin gene, PPAR-delta and the like. The misuse of these genes with the aim of increasing physical abilities has already become part of sport and is extremely difficult to identify, since genes and gene sequences entering the human body are proteins that are already structural and functional parts of the organism. On the other hand, viral vectors as the instruments for gene transfer attack and destroy the human immune system, and the reaction of the human body can be negative, with a danger of insertional mutagenesis and the appearance of oncogenes. Gene therapy might actually be much more useful in treating sports injuries, but even these procedures are still far from clinical practice. There is a fine line between gene therapy and gene doping in athletes. A number of growth factors will enhance repair, but it happen that expression of these factors increase the strength of bones and tendons, so that giving an advantage to competitors. First of all, it is necessary to acquaint athletes as much as possible with the negative consequences of using gene therapy. However victory and glory may be strong achievements, the health of these young people, and respect for fundamental and ethical principles, humanity, and fair play game have a more lasting value and represent the heavier weight on the scales.