Pregnenolone (PREG) can potentially be abused by athletes to maintain an equilibration of the steroidal environment after sex steroids administrations. Five men volunteers orally ingested 50 mg PREG to determine optimal urinary markers for detection of this steroid. Our findings show that ingestion of PREG has no significant effects on the testosterone/epitestosterone (T/E) and testosterone/luteinizing hormone (T/LH) ratios, whereas variable changes on the carbon isotopic values of three T metabolites: androsterone, etiocholanolone, 5beta-androstane-3alpha,17beta-diol (5beta-androstanediol) together with 16(5alpha)-androsten-3alpha-ol (androstenol) and 5beta-pregnane-3alpha,20alpha-diol (pregnanediol) have been observed. The difference between the carbon isotopic values (delta13C-values) of androstenol and pregnanediol is potentially the most reliable marker of exogenous PREG administration in males. For all subjects, the differences differ by 3.0 per thousand or more over a period of about 10 h and for both of them the detection window for positivity is extended over 40 h.