In late reproductive-aged breast cancer survivors, there is a need for real-time biomarkers of postchemotherapy ovarian function. The objective was to determine whether antimullerian hormone (AMH) and inhibin B are such biomarkers. The authors tested whether AMH and inhibin B were impacted by breast cancer treatment by comparing cancer survivors to age-matched control women and determined the association between these hormones and postchemotherapy menstrual pattern. Breast cancer patients (n = 127) with American Joint Committee on Cancer stage I to III disease who were premenopausal at diagnosis were enrolled postchemotherapy and observed. The primary endpoint was chemotherapy-related amenorrhea (CRA) (> or = 12 months of amenorrhea after chemotherapy). Matched pair analyses compared AMH, inhibin B, and follicle-stimulating hormone (FSH) levels between cancer and age-matched control subjects. Associations between hormones, CRA status, and change in CRA status over time were assessed. The median age of the patients at chemotherapy was 43.2 years (range, 26.7-57.8 years). At enrollment, median follow-up since chemotherapy was 2.1 years, and 55% of subjects had CRA. Compared with age-matched controls, cancer subjects had significantly lower AMH (P = .004) and inhibin B (P < .001) and higher FSH (P < .001). AMH (P = .002) and inhibin B (P = .001) were found to be significantly associated with risk of CRA, even after controlling for FSH. AMH was significantly lower (P = .03) and FSH was significantly higher (P = .04) in menstruating subjects who developed subsequent CRA. AMH and inhibin B are 2 additional measures of postchemotherapy ovarian function in late reproductive-aged breast cancer survivors. With further research and validation, these hormones may supplement limited current tools for assessing and predicting postchemotherapy ovarian function. Copyright 2009 American Cancer Society.