Preoperative ultrasound was used as an alternative to x-ray mammography to localize 92 breast lesions encountered in 82 patients. Recommendation for biopsy was made based upon the ultrasonographic finding of a nonpalpable mass or an area of architectural distortion, or in the presence of equivocal physical findings if sonomammography demonstrated a solid or anechoic mass. Sonomammography was performed in the operating room, just prior to anticipated biopsy, using a hand-held, high resolution scanner. When the suspicious area was imaged, and its precise location noted, the breast was then prepped and draped in the usual manner, and biopsy performed. If the suspicious area could not be easily localized after the incision was made and the breast explored, the transducer was "gowned" and used directly in the wound to help find the lesion. This technique has proven effective and accurate. In selected patients, ultrasound may be used instead of, and as well as, x-ray needle localization for the precise excision of non-palpable breast masses and areas of parenchymal distortion. Microcalcifications must still be addressed by x-ray mammography and needle localization with specimen radiography.