Color Doppler technique has been available for several years. The sensitivity of the equipment has improved and allows for assessment of tumor vascularity. We investigated multiple parameters in 258 patients, with 176 benign and 82 malignant lesions to define characteristic flow criteria. Median (25-75% quartiles and p-values are given for benign vs. malignant lesion. Number of tumor vessels: 2 (1-2) vs. 8 (5-14), p < 0.0001; mean peak systolic flow velocity: 11.1 cm/s (6.4-14.9) vs. 18.8 cm/s (13.7-25.1), p < 0.0001; maximum flow velocity: 12.5 cm/s (6.7-18) va. 32.5 cm/s (22.5-47.3), p < 0.0001; sum of all systolic flow velocities: 18.9 cm/s (7-34.2) vs. 147 cm/s (71.3-266.7), p < 0.0001; minimum systolic flow velocity: 8.9 cm/s(5.4-12.1) vs. 9 cm/s (6.3-11.3), p > 0.05; maximum RI: 0.71 (0.65-0.78) vs. 0.88 (0.78-0.99), p < 0.0001; minimum RI: 0.65 (0.57-0.68) vs. 0.64 (0.53-0.71), p > 0.05; average A/B ratio: 3.1 (2.7-3.7) vs. 4.3 (3.2-7.7), p < 0.0001; maximum A/B ratio: 3.4 (2.9-4.6) vs. 8.4 (4.5-9.9), p < 0.0001; minimum A/B ratio: 2.8 (2.3-3.2) vs. 2.9 (2.2-3.5), p > 0.005. The data analysis shows that flow resistance in malignancies is increased. This is in contrast to gynecological malignancies, where an increased diastolic flow indicates that flow resistance is decreased.