Evaluation of flow in nodular tumors of the breast may be performed by Doppler and computerized frequency analysis. In 46 nodules of the breast (22 malignant) the nodular flow velocity and frequency analysis revealed a faster flow with a significantly higher peak frequency and mean velocity. The intensity of sound which may be considered an index of the entity of flow in the nodule was larger than that observed in the normal surrounding breast tissue. In malignant nodules and generally in fast growing nodules the flow velocity and intensity was even larger. The flow intensity and velocity was also well correlated with the growth rate as reported by single patients. In elder patients a slow rate of growth even in tumors of larger size was associated with a significantly increased flow in comparison with the normal breast tissue but this increase was not particularly large when compared with fast growing nodules in younger subjects. In conclusion the evaluation of flow characteristics (mainly velocity, frequency analysis and intensity) may be a useful index of the growth rate of nodular tumors of the breast and these data may be useful to evaluate and monitor the evolution and pathophysiology of these nodules.