There is a potential need for the official criterion of testosterone abuse in sport (the urinary concentration ratio of testosterone glucuronide/epitestosterone glucuronide, TG/EG > 6) to be backed-up by some complementary markers, more particularly in cases of physiologically high TG/EG and when there is suspicion of joint administration of testosterone and epitestosterone. Testosterone, epitestosterone, their glucuro- and sulfoconjugates, 5-androstene-3 beta, 17 alpha-diol glucuronide and 17-hydroxyprogesterone have been analysed by isotope dilution-gas chromatography-mass spectrometry in plasma and urine of seven subjects supplemented with a single oral dose of undecanoates of testosterone and epitestosterone (respectively 40 mg and 1.5 mg). Adequate plasma criteria for testosterone abuse were the ratios of testosterone glucuronide/17-hydroxyprogesterone and testosterone glucuronide/testosterone which increased significantly above basal values for up to 10 h. The same trend was observed for the ratio of urinary glucuronides of testosterone/5-androstene-3 beta, 17 alpha-diol, while TG/EG was not affected by simultaneous administration of epitestosterone. One subject with low basal TG/EG failed to respond to testosterone administration by any significant increase of analysed parameters.