Urinary testosterone to epitestosterone ratio (T/E) is used as a marker for illegal exogenous testosterone use. Mean value in healthy adults is 1.13 and 6 is the upper limit of the accepted range. Urinary excretion of these two steroids were studied in 57 children and teenagers at different pubertal stages, using gas chromatography coupled with mass spectrometry with selective ion detection. Urinary excretion of testosterone and epitestosterone increased significantly during puberty. Mean T/E ratio remained fairly constant but interindividual variations were marked and in one subject the T/E ratio exceeded 6. These data suggest that this test may yield false-positive results in adolescents.