Cancer survivorship has significantly increased, however, treatment can cause infertility and ovarian endocrine failure in females due to the depletion of primordial follicles. We have previously reported that the pro-apoptotic BH3-only protein, PUMA, is a critical initiator of TAp63-mediated apoptosis in the ovary following DNA damage induced by γ-irradiation. In this study we investigated the impact of PUMA loss on the ovarian reserve following treatment with commonly used chemotherapeutic agents. Adult female Puma-/-or wild-type (WT) mice were injected with saline (control), cisplatin (Cis) 5 mg/kg, or cyclophosphamide (Cy) 300 mg/kg (N=5/group). Ovaries were harvested after 5 days and follicles counted. In WT females, primordial follicle numbers were reduced by 96% following treatment with Cy and by 73% following Cis. In contrast, Puma-/- females retained 100% of their primordial follicles following either treatment. A second cohort of mice was treated similarly, then mated with proven males. Both Cy- and Cis-treated WT females had a shortened fertile lifespan (Cy WT: -192±6 days; p<0.0001; Cis WT: -95±34 days); Cy-treated WTs had fewer litters (-4.11±1.05 pups; p<0.01). This fertility defect was ameliorated by loss of PUMA (age at last litter; control Puma-/-: 283±20 days vs Cy Puma-/-: 320±8 days, p=0.19; number of litters; control Puma-/-: 7±1.09 vs Cy Puma-/-: 7.33±1.20, p=0.85). Offspring of all groups were grossly normal. We are currently investigating the mechanisms underlying primordial follicle loss induced by chemotherapeutic agents. Preliminary results show that DNA damage (γH2AX immunostaining) and PUMA expression (in situ hybridization) are induced in primordial follicle oocytes of WT females within 8 hours of Cis or Cy treatment. Overall, we show that PUMA is the critical initiator of apoptosis in the ovary following chemotherapy, and its elimination prevents follicle loss and preserves fertility. These findings may translate into novel targeted approaches to prevent infertility following chemotherapy in women.