We report on our experiences of 598 drill biopsies in 581 female patients. The method is suitable for clarification of dubious palpatory findings in the breast, for verification of relapse, and for receptor analysis in individual cases. It is simple to carry out, almost free of complications and provides sufficient tissue for rapid-section diagnostics. It has a high precision (90% to 92%): no false positive results were noted. The advantage, compared to excision biopsy, consists of the shortening of the duration of operation and anesthesia and better diagnostic clarification. The problem of the excision cavity is avoided. In case of a mastectomy or quadrantectomy, the primary tumor and remains connected with the tissue surrounding the tumor is available in toto for histological examination. The risk of tumor cell dissemination from drillbiopsy did not appear to be increased. The limitations of the method apply to small (less than 1 cm) not definitely palpable tumors near to the thorax wall in large, voluminous breasts. The diagnosis of specific histological types requires a high degree of experience in ultrastructural appraisal of breast tissue. A negative drill biopsy should be followed by an excision biopsy, where a carcinoma is suspected.