Two methods of obtaining a preoperative diagnosis of breast lumps have been evaluated by simultaneous use on 131 patients. Tru-Cut needle biopsies gave a reliable diagnosis in 75 per cent of those suffering from primary carcinoma of the breast. No cases of benign disease were wrongly reported as carcinoma by this method. Fine-needle aspiration cytology gave no helpful information in one-half of the patients with malignant disease and in addition 5 cases of benign disease were falsely reported as carcinoma. Tru-Cut needle biopsy is a valuable preoperative investigation in patients with primary carcinoma of the breast.