The radiological detection of calcification is compared using xeroradiography, non-screen film and a film-screen combination. The "threshold" values of the smallest detectable size of calcification, under simulated clinical conditions, are found to be approximately 100 mum for xeroradiography and 400 mum for both the film techniques in this study. The incidence of calcification seen on the preoperative mammograms of patients with carcinoma of the breast is 48-5 per cent. Further calcification revealed by histological examination raises the overall incidence of calcification in mammary carcinomas to 63 per cent. The incidence on preoperative mammograms in benign breast disease is 20 per cent. The radiological features of calcification occurring in malignant and benign breast lesions are recorded, and no definitive distinguishing features are established. The histological appearance of calcification in malignant and benign breast disease is discussed.