Ans: A. Serum FSH(Ref. Ganong 25Ie p419, 425, 24Ie p427)Prior to initiating treatment for a couple, in whom the man has azoospermia, it is impoant to distinguish whether the lack of sperm in the ejaculate is from an obstructive or non-obstructive process.The presence of normal volume testes with bilaterally indurated epididymis and/or absent vas deferens will point to an obstructive etiology for azoospermia.A history of cryptorchidism in the presence of small or soft testes suggests non-obstructive azoospermia, especially if associated with an elevated serum (FSH) level.A decreased spermatogenesis leads to decrease in production of inhibin, which causes an elevation in FSH.