ITT-5 Mechanisms of Spermatogenesis in Man

Inclusion Criteria: * Males age 18-55 * In general good health based on normal screening evaluation * Normal serum testosterone, lutenizing hormone (LH) and follicle stimulating hormone (FSH) * Prostate Specific Antigen (PSA) \< 3.0 * Agrees not to donate blood or participate in another research study during the study * Informed consent * Must be willing to use a reliable form of contraception during the study Exclusion Criteria: * Participation in a long-term male contraceptive study within the past three months * History of testosterone or anabolic steroid abuse in the past * History of or current skin disorder that will interfere with testosterone gel * Poor general health or significantly abnormal screening blood results * History of or current testicular or prostate disease * History of a bleeding disorder or need for anticoagulation * History of untreated sleep apnea and/or major psychiatric problems * BMI \> 32 * History of or current liver disease * Chronic pain syndrome * Current use of terfenidine, astemizole, cisapride, budesonide, felodipine, fluticasone, lovastatin, midazolam, sildenafil, or vardenafil * Use of glucocorticoids or underlying adrenal insufficiency * Active drug or alcohol abuse within the past year