19-Norandrosterone (19-NA) and 19-noretiocholanolone (19-NE) are the two main indicators used to prove the illegal use of nandrolone by humans. Recent studies showed that 19-NA and 19-NE can be endogenously produced in some individuals. The mediated cases observed over the last three years generated some questions about the appropriateness of the official International Olympic Committee cutoff level, which is 2 ng/mL of 19-NA in male urine samples. In the present study, professional soccer players belonging to the French First League were studied over a period of 19 months. In total, 385 urine samples were taken immediately before and after soccer competitions and were coupled with 200 blood samples for testosterone and LH determination. Results of the study showed that the mean values for 19-NA and 19-NE were 0.097 ng/mL and 0.033 ng/mL, respectively. For 19-NA, 70% of the samples proved to be below 0.1 ng/mL, whereas less than 20% were found to be between 0.1 and 0.2 ng/mL, and 7% were between 0.2 and 0.3 ng/mL. Only four urine samples were above 1.0 ng/mL; the maximal value was 1.79 ng/mL. For 19-NE, only one sample was above 1.0 ng/mL; the value was 1.42 ng/mL. Concentrations of these compounds after games were generally significantly higher than those before games.