Interest in breast-conserving treatment of mammary carcinoma has increased tremendously in recent years, as breast cancer is being detected at an earlier stage than previously, especially in regions where screening is practised. In the present report it is argued that the breast-conserving procedure is still an experimental method which should be performed only within the framework of clinically controlled studies. An uncritical use of the method could render its improvement difficult and prevent an accurate assessment of its possibilities for cure. A short description is given of a recently started Danish multicentric study in which the result of breast-conserving therapy, randomly, is weighed against the result of mastectomy. The preliminary experience of the method obtained in the Odense Centre is submitted. Since 1979 a total of 44 patients have had breast-conserving therapy for mammary carcinoma. Their median age was 47 years, range 30-69 years. About 10% had stage II cancer. So far, local recurrences in the breast have not been observed within the follow-up period, 5-48 months, but one case of axillary recurrence. Metastatic disease has not been demonstrated.