From 1977 to 1983 we have used electric drill needle biopsy of suspicious masses in the breast in 437 patients. In 104 patients with primary breast carcinoma 94 were diagnosed correctly by the initial biopsy, 9 were found on the second or third biopsy and one on the subsequent excisional biopsy. The rate of accuracy of the initial biopsy was 90.4 per cent. The diameters of the 104 carcinomas were less than 2 cm in 62 (59.6 per cent), 2-5 cm in 39 (37.5 per cent) and 5 cm or more in 3 (2.9 per cent). There were 17 patients (16.3 per cent) with a tumor 10 mm or less in diameter. Three hundred and thirty three patients had benign lesions. This drill needle biopsy method can be performed easily and accurately on nodules less than 2 cm, or even 10 mm or less nodules. For a diagnosis of early breast carcinoma made in the outpatient clinic or in screening examination programs, this method may be the most appropriate.