Three study drugs will be used in this study: Testim (testosterone gel), Human Chorionic Gonadotropin (hCG) and acyline. Testosterone is a naturally occurring hormone in men. When given to normal men, testosterone gel will temporarily lower the amount of testosterone in the testes and lower sperm counts. hCG is a female hormone produced during pregnancy that is similar to and has the same actions as a male hormone, luteinizing hormone (LH). Like LH, hCG stimulates the testis to produce testosterone and sperm, and is used in the treatment of men who are deficient in LH. When hCG is given together with testosterone to normal men, the amount of testosterone in the testes will change, dependent on the amount of hCG received. Some participants will receive placebo hCG injections (no active medication).