The aim of the study was to ascertain the reliability of a Doppler signal in the diagnosis of breast cancer. Computerized blood flow analysis was performed on 117 patients who presented with a breast lump at the Division of Diagnostic Oncology of the Istituto Nazionale Tumori of Milan. The values of systolic peak and diastolic frequency were evaluated in relation to the histologic diagnosis. Ten patients had a spontaneous regression of the lump and were excluded from the study. The number of evaluable cases with histologic confirmation was 107: 69 carcinomas and 38 benign lesions. Systolic peak values for the 69 carcinomas ranged from 1500 to 7400 Hz, with a mean value of 3243.4 Hz; diastolic frequency ranged from 200 to 3700 Hz, with mean value of 1413.9 Hz. No diagnostic signals were found in 4 breast cancers (false negatives). Twenty-three of 38 benign lesions (60.5%) and 65 of 69 malignant nodes (94.2%) were correctly diagnosed. The Doppler signal with computerized spectral analysis in addition to more specific ultrasonographic parameters could be considered a useful tool in the diagnosis of breast cancer.