Near infrared reflectance spectroscopy is routinely used for the analysis of quality components of feedstuffs. Near infrared spectrophotometers, coupled with a fiber optic probe, could enable direct measurements of the live animal. This study was conducted to characterize changes in the vulva and vestibule during the bovine estrous cycle using near infrared (NI) spectroscopy. Sixteen cycling Holstein cows were observed for estrus twice daily from 40 days postpartum for three estrous cycles or until conception was verified. In addition, weekly rectal palpations, cowside milk progesterone tests, and tailhead chalk were used to aid in estrous detection. Near infrared spectra of both the vulva and the vestibule were collected daily (Model 6500 with 1.83 m fiber optic probe, NIR Systems Inc., 1100 to 2500 nm). Twenty-four estrous periods were confirmed. Vulvar and vestibular spectra of estrous and nonestrous cows were compared. Spectral differences occurred in three regions at 1700 nm, 1790 nm, and 1800 nm (P<.05). These regions are possibly associated with changes in carbohydrate, protein, and water content. Results indicate that direct NI analysis of the live cow is possible and changes in the vulvular and vestibular tissue during the estrous cycle can be detected. However, accurate estrous detection using NI interactance is not practical at the present time because of individual cow variability.