Perfusion of enlarged lymph nodes by colour-coded sonography was studied prospectively in 105 benign and 115 malignant lymph nodes. The diagnosis was confirmed histologically in 158 and clinically in 62. Spectral analysis in the benign lymph nodes provided normal values for pulsatility and resistance indices. A pulsatility index greater than = 1.8, or a resistance greater than = 0.9 indicate lymph node metastases with positive prediction of 93% and specificity of 97%. In addition, subjective, semiquantitative classification of lymph node perfusion in relation to the surrounding fat or connective tissue improves the diagnosis of lymph node metastases and of malignant lymphomas.