The Evaluation of the Survival Rate and Motility of Freeze-Thawed Mouse Sperm -Frozen in and out of the Epididym. Saki GH, Hashemitabar M, Ghavvamizadeh B, Safikani Z, Bijannejad D, Sobhani A Corresponding Authoŕ s Address: Department of Anatomy, Tehran,University of Medical Science, Tehran, Iran. Email: Sobhania@Tums.ac.ir Background & objectives: Direct contact between a sperm cell and cryopreservation solution has detrimental effects on the cell. In this study the role of the epididymal tissue in the preservation of direct contact between sperm cell and cryopreservation solution during a freeze–thaw process was studied by assessing motility and vitality of the sperm. Material & methods: About 30 male mice were killed and the right caudal epididymis were removed and placed in cryo-preservation solution for two minutes. The samples were exposed to liquid nitrogen vapor for ten minutes and then immersed in liquid nitrogen. The left caudal epididymis were similarly removed and placed in T6 medium. In order to extract sperm, samples were needled and incubated for 1 hour at 37ºC. Subsequently, sperm motility and vitality were assessed as control group and then the remaining solution was transmitted into a tube containing cryopreservation solution. For thawing, samples were picked up from a liquid nitrogen tank and kept in room temperature for 20 seconds and then immersed in warm water (37ºC) for 2 minutes. Thereafter, sperm motility and vitality were assessed. Results: The survival rates of the three groups (control, outer and inner epididym) were 78.75±13.01, 34.67±7.86 and 9.97±7.08, respectively. The statistical analysis has shown that the difference between the inner and outer epididym was significant (P<0.05). The progressive motility of sperms in the three groups was 30.29±15.33, 3.29±3.55 and 0.00±0.00, respectively. The progressive motility of sperms in the inner and outer epididym was less than the control group (P<0.05), but there was no significant difference between the inner and outer groups (P=0.344). The non-progressive motility of sperms in the three groups was 34.72±12.21, 29.21±10.37 and 6.78±4.94, respectively. The statistical analysis has shown that the difference between the control and outer groups and also between the control and inner groups was significant (P<0.05) but the difference between the inner and outer groups was not significant. Conclusion: The quality of cryopreserved–thawed sperm in the outer epididym group was significantly better than in the inner epididym group. In this study we can conclude that the epididym has no protective effect on sperm during cryopreserved processing.