['To study the potential role for using serum biomarkers, including insulin-like factor 3 (INSL3), 17α-hydroxyprogesterone, antimüllerian hormone, and inhibin B, as correlates of intratesticular T (IT-T) concentrations in men.', 'Prospective, randomized, controlled trial.', 'University-based medical center.', 'Thirty-seven healthy men aged 18-50 years.', 'All men received the GnRH antagonist acyline, plus very low doses of hCG (0 IU, 15 IU, 60 IU, or 125 IU) SC every other day or 7.5 g T gel daily (75 mg delivered). The IT-T concentrations obtained by percutaneous testicular aspiration with simultaneous serum protein and steroid concentrations were measured at baseline and after 10 days of treatment.', 'Intratesticular and serum hormone and gonadotropin concentrations.', 'After 10 days of gonadotropin suppression, serum INSL3 decreased by more than 90% and correlated highly with IT-T concentrations. In contrast, serum inhibin B, antimüllerian hormone, and 17α-hydroxyprogesterone did not correlate with IT-T. Serum INSL3 increased with the dose of hCG administered and returned to baseline after treatment.'] Is serum insulin-like factor 3 highly correlated with intratesticular testosterone in normal men with acute , experimental gonadotropin deficiency stimulated with low-dose human chorionic gonadotropin : a randomized , controlled trial?