Liposomes are biocompatible materials that show promise as vehicles for drug delivery, inhibitors of cell adhesion, and carriers for the introduction of genetic material into cells. In this paper, we describe the synthesis and characterization of a new class of polymerized liposome particles (paramagnetic polymerized liposome (PPL), Figure 1) that have lanthanide ion chelates as head groups and that can be easily visualized using magnetic resonance imaging (MRI). The R(1) molar relaxivity was found to depend primarily on the linker length (m) and on the surface metal density and only weakly on particle size. PPLs containing 10 mol % of compound 1b (m = 2) and 90 mol % of compound 3 had a R(1) = 12.2 mM(-1) s(-1), while PPLs with 10 mol % compound 1a (m = 1) and 90 mol % of compound 3 had a R(1) = 5.7 mM(-1) s(-1). PPLs with 10 mol % of compound 1a and 90 mol % of compound 4 had a R(1) = 8.9 mM(-1) s(-1), while PPLs with 50 mol % of compound 1a and 50 mol % of compound 4 had a R(1) = 4.3 mM(-1) s(-1). A biotinylated lipid (compound 2) was also incorporated into the particle without affecting R(1) relaxivities for use as a marker for histochemical studies. We have also for the first time used atomic force microscopy (AFM) to investigate the size and nature of these particles in an aqueous environment. We feel that these new materials may prove useful for the in vivo investigation of liposome formulations as vehicles for therapeutic applications and for evaluating tissue pathology with MRI.