MR images of the iliac lymph nodes of 25 VX2 carcinoma-bearing rabbits and of 5 tumor-free rabbits were obtained at 1.5 T before and after endolymphatic administration of superparamagnetic iron oxide particles (SPIO) at a dose of 1 mumol Fe per extremity. Imaging results were correlated with histology. In unenhanced images intranodal metastases were not detectable with any of the pulse sequences used and the signal intensities of tumor-free and metastatic lymph nodes did not differ significantly. After administration of the contrast medium, a significant signal loss (p < or = 0.05) occurred in the healthy lymph node tissue, whereas the signal intensity of lymph node metastases remained unchanged. In SPIO enhanced images, the threshold size for detection of lymph node metastases was 2 mm. Metastatic involvement was detected in 28 of the 30 tumorous lymph nodes with the SE 2000/15 sequence but in a smaller number of lymph nodes with the sequences SE 500/22 (n = 27) and 2000/65 (n = 21).