SummaryThis study aimed to assess the morphological changes in neonate vitrified testicu-lar grafts after host treatment with melatonin. Neonate vitrified testes, candidatesfor transplantation to treated and nontreated groups receiving melatonin, werethawed in media containing or not containing 100 l M melatonin. Followingtransplantation, melatonin (20 mg kg 1 per day) and saline were given to thetreated and nontreated groups for up to 9 weeks. The testicular status wasassayed by terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridinetriphosphate (dUTP)-biotin nick-end labelling TUNEL, semi-thin section andultra-structure studies. Chi-squared test was used to compare categorical vari-ables between the groups. Overall, the degenerative and apoptosis changes in thevitrified testis parenchyma were not significant. However, atrophic seminiferouscords and jumbled appearance of the interstitial space were more often observedin the nontreated group than in the treated ones. Semi-thin sections showed thatthe germinal epithelium was taken in a normal arrangement on the testiculargrafts of both groups. Nevertheless, ultrastructural analysis revealed that thecharacteristics of interstitial space cells, basement membrane BM and epithelialcells of seminiferous tubules in the treated group were better than those in thenontreated group. The study revealed a beneficial effect of melatonin on vitrifiedneonatal testes and after that, on restoring testicular grafts.IntroductionThe natural spermatogenesis process in the testes of can-cer patients treated with radiotherapy and chemotherapyis may be disrupted and lead to a loss of fertility (Agarwal& Allamaneni, 2005).In general, freezing of semen with subsequent assistedreproductive technology (ART) is a method that can helpcancer patients overcome this problem (Lass et al., 2001).However, these techniques can only be used in adult casesand those who have partners. It should be noted that about2% of all malignant cancers occur during childhood andinfancy (Brougham & Wallace, 2005). Furthermore, somestudies reported that freezing of semen with subsequentART among the treated cancer patients did not give a goodresult in restoration of fertility (Blackhall et al., 2002).Spermatogonia stem cells lack acrosome and also theirmetabolic activity is relatively inactive. In addition, dueto the large size of spermatogonia stem cells, the influ-ence of cryoprotectives (CPA) through freezing isneglected, and cytogenetic abnormalities are less observed(Schlatt et al., 2002). Therefore, it seems that these cellsare more resistant to the damage caused by the freezingprocess in comparison with mature spermatozoa (Cozzo-lino & Lamb, 2000). Therefore, over the past few years,researchers’ attention has been shifted to use of these cellsor testis parenchyma for freezing and transplantation ininfertile men. These techniques have been introduced assuitable methods that can restore the impaired reproduc-tive and testicular activity of cancer patients who haveovercome the disease (Neri et al., 2009).However, despite the introduction of new methods formanaging freezing and selection of suitable sites for trans-plantation, the quality and quantity of spermatogoniastem cells and parenchyma of the grafted testes are notsatisfactory (Wyns et al., 2008; Neri et al., 2009). Because