Liposomal drugs offer the promise of an improved therapeutic index due to improvements in the specific delivery of anti-cancer agents to tumors. The presented work concentrates on imaging the tumor uptake of /sup 111/In-labeled liposomes noninvasively as a specific tumor drug delivery carrier in a murine cancer model. The tumor uptake of liposomes has been imaged using a microSPECT/microCT small animal dedicated scanner prototype constructed at our laboratory. The imaging system consists of a high resolution SPECT (700 /spl mu/m) and high resolution CT (70 /spl mu/m). The SPECT subsystem consists in specially designed CZT gamma cameras shielded for energies up to 250 keV. The mice were injected with liposomes and scanned at the time of maximum tumor uptake (24 h). The total activity of the mouse samples was of the order of 250 uCi, and with tumor sizes of 1000-1500 mm/sup 3/. The imaging geometries in the CT and SPECT acquisitions were selected to obtain high magnification and high efficiency to image the tumor located within the torso. The SPECT and CT projections were taken sequentially. The acquired images show that necrotic tumors can de imaged with high resolution to observe liposome inhomogeneous uptake.