Future detection of breast cancer will probably be based on tissue function such as altered vascularity and blood flow. Assessment of tumour blood flow and its pattern may be significant for prognostic prediction, and early evaluation of treatment response. An ideal method of assessment of perfusion would therefore measure a wide area of the breast without the necessity for surface contact. A possible method for achieving this ideal is the recent development of a laser Doppler imager (LDI) that creates an image of tissue perfusion. The method is based on the recording of Doppler shift caused by movements of red blood cells in the backscattered light of a laser beam that successively scans a certain tissue area. This method reflects the vascularity of overlaying skin. We have applied this technique to 101 patients, 47 normal, 25 benign, and 29 carcinoma. Our findings were correlated with breast imaging and tissue diagnosis. The mean blood flow in 'normal' patients was 299 +/- 155 and 311 +/- 157 flux (+/- SD) for right and left breast, in patients with benign breast change it was 482 +/- 209 flux and in patients with carcinoma it was 711 +/- 280 flux. Patients with benign breast change have higher skin blood flow than symptomatic normal patients but the highest levels have been recorded in patients with breast cancer. We believe that LDI may have an important role in improving our understanding of the physiology of the normal breast and may provide a practical method of monitoring breast skin blood flow changes in clinical situations.