The correlation between clinical findings, mammography and thermography on the one hand and histological structure of the breast on the other hand, was investigated in 133 women. Palpable changes in the breast parenchyma indicated excision biopsy in all cases. The following criteria were employed for palpatory assessment: size, differentiation, nodular mobility and consistency. For mammography, criteria such as calcification, opacity, contralateral comparison and skin thickening were used. For thermography, a modified "Gautherie score" was employed. All three palpatory parameters, however, do not provide reliable differentiation between benign and malignant tumours, since the palpatory findings in fibrocystic disease are similar to those in large malignant growths. Small malignant growths, in turn, may resemble benign tumours. Furthermore, the group of fibrocystic disease markedly reduces the specificity of the radiological findings. However, as aid to differential diagnosis it may be said that apart from the shape of the shadow, contralateral difference in appearance is more likely to occur with benign and malignant tumours than with fibrocystic disease. With regard to thermography a low score i.e. an unconspicuous picture of heat distribution is unlikely to signify a malignant growth. It is, however, impossible to distinguish between mastopathy and malignant tumour. Additional investigations i.e. mammography and thermography do not rule out the existence of a malignant growth.