The scanning electron microscope was used to evaluate the effects of ultrasonic irrigation before and after root conditioning. Six groups of five specimens each received saline irrigation; ultrasonic irrigation; saline irrigation followed by root conditioning with either citric acid or tetracycline hydrochloride; or ultrasonic irrigation followed by root conditioning with either citric acid or tetracycline hydrochloride. After immersion in citric acid or tetracycline hydrochloride solutions, root dentin was rinsed again with saline or irrigated ultrasonically. Control specimens exhibited an amorphous, irregular surface smear layer. Ultrasonic irrigation, citric acid, and tetracycline hydrochloride were effective in removing the smear layer. use of ultrasonic irrigation before and after acid application improved the exposure of dentinal fibrils.