The study design included six visits. During the first visit (visit 0), the subjects underwent physical examination(height, weight, body mass index (BMI), arm span, and upper segment measurement) and testicular ultrasound (US) for the calculation of testicular volume. At 0800 h of day 0, all subjects provided a basal blood sample immediately followed by a single intramuscular injection of hCG of 5000 IU. Further five visits were performed each of five following consecutive days after the hCG injection. A blood sample was taken at each visit after an overnight fast

Blood samples were centrifuged at 2955 g for 15 min. Sera were transferred into plain polypropylene tubes and stored at -20°C until assayed. P, 17OHP, AS, DHEA, and TS were determined by LC-MS/MS at the laboratory of the Centre for Applied Biomedical Research of the S. Orsola-Malpighi Hospital, Alma Mater Studiorum, University of Bologna, Bologna, Italy.

Inclusion Criteria:

• Klinefelter syndrome diagnosis at kariotype evaluation for the study group
• Healthy age-matched men in the control group

Exclusion Criteria:

• previous or ongoing androgen therapy