Malignant growth requires a high metabolism. This allows the differentiation of lesions by Doppler measurements of their vascularisation. In this study of 224 patients with 45 malignancies (37 breast cancers and 8 local recurrences), 87% of the cases were correctly identified. Differentiation of palpable lesions was possible in 93%. The flow in normal breast arteries was studied as well as in carcinomas, comparing continuous-wave (CW) Doppler with frequencies at 4 and 8 MHz. To improve flow evaluations in nonpalpable lesions, pulsed Doppler was used at 3 MHz and color mapping systems at 5 MHz in another 37 patients. Color Doppler at 5 MHz identified 17 of the 21 malignancies; in all cases pulsed Doppler at 3 MHz failed.