In vivo OCT images of the vagina in a sheep model were obtained using a clinical endoscopic OCT system (Imalux, Cleveland, OH). Images were obtained after vaginal lavage at baseline (before treatment) and 24 h after treatment with 5 mL intravaginal 2% nonoxynol-9 (N9, Gynol II, Johnson & Johnson Professional Products) or hydroxyethylcellulose placebo (HEC, ReProtect, Baltimore, MD).3 N9 is an over-the-counter spermicide that has been shown to disrupt and thin the epithelium and increase suspectibility to HIV;2,5 therefore, we used this treatment, known to cause epithelial toxicity, to test the performance of our segmentation algorithm. Twenty representative OCT images from three N9-treated sheep and one placebo-treated sheep were selected for image processing. Vaginal biopsies were obtained at the site of OCT imaging to confirm findings. The biopsies were fixed in formalin and stained with hematoxylin and eosin. Student -test was used to compare epithelial thickness measurements, and alpha of 0.05 was used for significance.