Effect of Letrozole on Seminal Parameters in Men With Non Obstructive Azoospermia and Severe Oligozoospermia.

Inclusion Criteria * Patients with non-obstructive azoospermia (absence of sperm in the pellets of two centrifuged semen samples collected 30-60 days apart) * Patients with non-obstructive azoospermia who do not yield spermatozoa with fine needle aspiration (FNA) * Patients with severe oligozoospermia (presence of sperm concentration less than 5 million per ml in both semen samples collected 30-60 days apart) * Normal sperm appearance, consistency, liquefaction, volume and pH * Patient must not possess any chromosomal aberrations Exclusion Criteria * Possible etiology of infertility present * Seminal white blood cell concentration more than 10 million per ml * Positive seminal culture analysis * Positive urethral swab for chlamydia test * Smoker * Drug or alcohol abuse * Ongoing medical treatment (gonadotropins, anabolic steroids, cancer chemotherapy, non-steroidal anti-inflammatory drugs, previous cancer radiotherapy or chemotherapy) * Palpable varicocele * X-ray exposure in the previous 8 months * Y chromosome microdeletion * Karyotype abnormalities (Klinefelter syndrome)