At birth, all of a female mammal's oocytes arrest at prophase of the first meiotic division (the germinal vesicle stage). Coincident with ovulation in sexually mature female mice, the germinal vesicle breaks down, a polar body is formed by completion of the first meiotic division, and meiosis arrests for a second time at metaphase of the second division. Unless an ovulated oocyte is fertilized, it will not complete the second meiotic division. It is generally suggested that prophase I arrest is maintained by elevated levels of cyclic AMP (cAMP) in the cytoplasm of the oocyte, and maturation is triggered by reducing cAMP levels. An important factor that has been overlooked in oocyte arrest and maturation is the presence of AMP, the product of cAMP hydrolysis by phosphodiesterase. AMP-activated protein kinase (AMPK) is believed to have an important role in triggering oocyte maturation. AICAR (5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside), a membrane soluble AMP analog, activates maturation in oocytes arrested by elevated cAMP (Downs et al., 2002). Denuded oocytes from CD-1 female mice were maintained at prophase I arrest in M2 medium by the presence of 5 mM theophylline, a phosphodiesterase inhibitor. Theophylline-arrested oocytes were cultured in 250 μM and 500 μM AICAR. Both concentrations significantly overcame prophase I arrest when compared to oocytes cultured in theophylline alone (p <0.0001, df=2). Although the 500 μM AICAR treatment yielded a greater response than the 250 μM AICAR treatment the difference was not significant (p=0.209, df=2). Because AMPK is known to be activated in response to oxidative stress, theophylline-arrested oocytes were cultured in either 5 μM menadione or 100 μM hydrogen peroxide. Both treatments significantly overcame prophase I arrest when compared to oocytes cultured in theophylline (p <0.0001, df=2). Menadione and hydrogen peroxide treatments were not significantly different from one another (p=0.080, df=2). These results support the hypothesis that the role of reduced cAMP levels in stimulating oocyte maturation is due, at least in part, to cAMP breakdown to AMP and subsequent activation of AMPK.