The results of thermographic examinations in 154 patients with various diseases of the breast using an AGA thermovision apparatus are described. An account of the apparatus and technique is given and the scope of the method, using isotherms at various temperature levels, is discussed. Carcinomas, metastases, fibroadenomas and inflammatory processes can be demonstrated by increased heat production which is not observed in other conditions (table). Thermography represents an addition to other methods of diagnosing breast diseases and deserves further clinical evaluation.