The report presents the case of a sportswoman who accused her coach of having administered to her doping substances. During the judicial proceedings, biological samples of urine and hair were collected from this sportswoman. In the urine sample, a nandrolone metabolite was detected, but the result of hair analysis was negative. The paper presents possible reasons for the presence of 19-norandrosterone in urine, as well as the difficulties associated with interpretation of 19-norandrosterone detection during the doping control.