Preoperative ultrasonography was used as an alternative to x-ray mammography to localize 92 breast lesions encountered in 82 patients. Recommendation for biopsy was made on the basis of 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 an anechoic mass. Sonomammography was performed in the operating room, just before anticipated biopsy, with a hand-held high-resolution scanner. When the suspicious area was imaged and its precise location noted, the breast was then prepared and draped in the usual manner, and a biopsy was 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 ultrasonography may be used as well as, or instead of, x-ray needle localization for the precise excision of nonpalpable breast lesions, excluding calcifications.