Palpable breast masses which have a nondiagnostic appearance on the mammogram often require a biopsy to rule out malignancy. Contact B-scan ultrasonography of such masses were performed in an effort to improve the diagnostic accuracy of mammography and reduce the number of unnecessary biopsies. A total of 200 patients with breast masses of 1-8 cm were examined by both methods. The results of this combined evaluation were compared to those of mammography alone. Of 115 pathologically proven lesions, 44 were fluid-filled cysts. Sonography correctly diagnosed all 44 cysts, while mammography was equivocal in 27 (61%) of them. Of the remaining 71 solid masses, 38 were benign and 33 malignant. Mammography alone correctly diagnosed 31 carcinomas (94%), whereas sonography correctly diagnosed 26 (78.8%). While the infiltrating carcinomas have a typical sonographic appearance, circumscribed carcinomas may have the same sonographic features as fibroadenomas; the value of sonography here was to establish whether the mass was solid. In other solid masses such as those produced by dysplasias, abscesses, and mastitis, sonography was helpful in differentiating between diffuse and discrete lesions. The combined mammographic-sonographic evaluation of breast masses was more accurate than either method alone.