Various biophysical methods have been utilized in the diagnosis of breast cancer. To date the best results have been obtained with x-ray mammography. Ultrasound and thermography have great appeal as non-destructive techniques but, in the present state of development, are of limited use. The spatial resolution presently obtainable in ultrasonograms is inadequate for the detection of subclinical cancer and thermography is also of questionable reliability. While an overall true positive rate of 70% to 75% may be anticipated with thermography, the bulk of false negatives would seem to occur in those tumors most amenable to therapy, i.e., subclinical cancers. The "false positive" rate of thermography is also excessive, but would be acceptable for establishing a high risk group if true positive rates could be improved. At present thermography finds its greatest use as an adjunct to mammography and physical examination; it should not be used as the sole modality in a screening program. The efficacy of mammography can be readily demonstrated but the propriety of its use as a screening device has been questioned. This is primarily related to the possible carcinogenic effect of radiation at diagnostic levels. Although the carcinogenic effect is unproven, the dose in radiologic procedures should be kept to a minimum consistent with adequate images. The present state of the art would indicate that the risk, if any, is minimal as contrasted with the natural incidence of breast cancer and the results of early diagnosis and treatment.