To subjectively and semiquantitatively evaluate color Doppler signals on images of breast lesions. A 5-MHz ultrasound (US) system was used to examine 210 new breast lesions. Signals were evaluated subjectively with an analog scale. A semiquantitative scoring system involved analysis of the average number of vessels per square centimeter and average density of color pixels. Vessels were detected in 57 of 58 cancers (mean, 0.11 vessels per square centimeter, occupying 1.76% of the scan area). Color Doppler scores had no correlation with conventional prognostic indicators such as lymph node status or survival. Fewer vessels per square centimeter (mean, 0.06) occupying a smaller area (mean, 0.41%) were detected in the five fibroadenomas (n = 36) that showed color Doppler signals. Most cases (99 of 104 [96%]) of benign breast changes had no color Doppler signals. Color Doppler signals in a lesion otherwise thought to be benign should prompt a biopsy, while the absence of signals in an indeterminate lesion is reassuring.