The aim of the study was a comparison of 2 novel macromolecular contrast agents, Gadomer-17 and Polylysine-Gd-DTPA, with commercially available Gd-DTPA in determining the quality of tumor microvasculature by dynamic contrast enhanced MRI. Three groups of 5 mice with SA-1 tumors were studied. To each group of animals one contrast agent was administered; i.e. the first group got Gd-DTPA, the second group Gadomer-17 and the third group Polylysine-Gd-DTPA. To perform dynamic contrast enhanced MRI a standard keyhole approach was used by which consecutive signal intensity change due to contrast agent accumulation in the tumor was measured. From the obtained data, tissue permeability surface area product PS and fractional blood volume BV were calculated on a pixel-by-pixel basis. PS and BV values were calculated for each contrast agent. Based on the values, contrast agents were classified according to their performance in characterizing tumor microvasculature. Results of our study suggest that Gadomer-17 and Polylysine-Gd-DTPA are significantly superior to Gd-DTPA in characterizing tumor microvasculature.