Objective: Slow cooling rates of 0.3°C/minute are usually used for human embryos, although rapid cooling rates are preferred to optimize time management in clinical laboratories. To achieve this goal, we have validated a preferred program that successfully freezes mouse embryos in 25 minutes.Materials and Methods: Mice (strain B6C3F1) were superovulated using a standard PMSG/hCG regimen. Embryos were cultured in Sage Fertilization media + 10% synthetic serum substitute (SSS, Irvine Scientific) in a low oxygen environment (5%02, 5%CO2 and 90%N2). Eight cell or compacted stage embryos (n=146) were divided into two groups and were either frozen rapidly, n=80, or slowly, n= 66, using Quinn’s Advantage Embryo Freezing and Thaw kits (Sage IVF Inc.).Embryo freezing followed the short exposure regimen recommended by Sage: 1.5 M propanediol, (PrOH) (10 minutes), then 1.5M PrOH + 0.1M sucrose (5 minutes) at room temperature. Straws (IMV 0.25ml) were heat sealed and placed in a Biogenics Freeze Control CL5500 or CL8000 programmable freezer.Rapid freezing program:Start temperature −6.5°C, manual seeding, hold for 1 minute, 0.90°C/minute to −30.0°C, plunge. Program duration, 25 minutes.Slow freezing program:Start temperature 20°C, 2°C/minute to −6.5°C, manual seeding and hold for 10 minutes, 0.3°C/minute to −35°C, plunge. Program duration, 105 minutes.Straws were held in liquid nitrogen overnight and thawed using a two step thaw: 0.5M sucrose (10 minutes) then 0.2M sucrose (10 minutes). Embryo survival (> 50% of cells) was assessed at the time of thaw and via blastocyst formation.Results: Survival rates were 91% (73/80) for embryos frozen rapidly and 80% (53/66) for embryos frozen slowly. Rates of development to blastocyst were 89% (65/73) in the rapid freeze group and 85% (45/53) in the slow freeze group. These differences were not significant using Chi Square analysis.Conclusions: Survival of embryos using the rapid protocol was not significantly different from the standard slow protocol. Embryo development to blastocyst further indicated embryo competency. This may be related to decreased exposure time of embryos to potentially toxic cryoprotectants. There are advantages in the clinical lab setting to having better time management procedures, especially if success rates are not compromised. Objective: Slow cooling rates of 0.3°C/minute are usually used for human embryos, although rapid cooling rates are preferred to optimize time management in clinical laboratories. To achieve this goal, we have validated a preferred program that successfully freezes mouse embryos in 25 minutes. Materials and Methods: Mice (strain B6C3F1) were superovulated using a standard PMSG/hCG regimen. Embryos were cultured in Sage Fertilization media + 10% synthetic serum substitute (SSS, Irvine Scientific) in a low oxygen environment (5%02, 5%CO2 and 90%N2). Eight cell or compacted stage embryos (n=146) were divided into two groups and were either frozen rapidly, n=80, or slowly, n= 66, using Quinn’s Advantage Embryo Freezing and Thaw kits (Sage IVF Inc.). Embryo freezing followed the short exposure regimen recommended by Sage: 1.5 M propanediol, (PrOH) (10 minutes), then 1.5M PrOH + 0.1M sucrose (5 minutes) at room temperature. Straws (IMV 0.25ml) were heat sealed and placed in a Biogenics Freeze Control CL5500 or CL8000 programmable freezer. Rapid freezing program: Start temperature −6.5°C, manual seeding, hold for 1 minute, 0.90°C/minute to −30.0°C, plunge. Program duration, 25 minutes. Slow freezing program: Start temperature 20°C, 2°C/minute to −6.5°C, manual seeding and hold for 10 minutes, 0.3°C/minute to −35°C, plunge. Program duration, 105 minutes. Straws were held in liquid nitrogen overnight and thawed using a two step thaw: 0.5M sucrose (10 minutes) then 0.2M sucrose (10 minutes). Embryo survival (> 50% of cells) was assessed at the time of thaw and via blastocyst formation. Results: Survival rates were 91% (73/80) for embryos frozen rapidly and 80% (53/66) for embryos frozen slowly. Rates of development to blastocyst were 89% (65/73) in the rapid freeze group and 85% (45/53) in the slow freeze group. These differences were not significant using Chi Square analysis. Conclusions: Survival of embryos using the rapid protocol was not significantly different from the standard slow protocol. Embryo development to blastocyst further indicated embryo competency. This may be related to decreased exposure time of embryos to potentially toxic cryoprotectants. There are advantages in the clinical lab setting to having better time management procedures, especially if success rates are not compromised.